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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.
- Catalyst accessibility and acidity in the hydrocracking of HDPE: a comparative study of H-USY, H-ZSM-5, and MCM-41 modified with Ga and AlPublication . Costa, Cátia S.; Ribeiro, M. Rosário; Silva, Maria JoãoPlastic pollution is a critical environmental issue due to the widespread use of plastic materials and their long degradation time. Hydrocracking (HDC) offers a promising solution to manage plastic waste by converting it into valuable products, namely chemicals or fuels. This work aims to investigates the effect of catalyst accessibility and acidity on the HDC reaction of high density polyethylene (HDPE). Therefore, a variety of materials with significant differences in both textural and acidic properties were tested as catalysts. These include H-USY and H-ZSM.5 zeolites with various Si/Al molar ratios (H-USY: Si/Al = 2.9, 15, 30 and 40; H-ZSM-5: Si/Al = 11.5, 40, 500) and mesostructured MCM-41 materials modified with Ga and Al, also with different Si/metal ratios (Si/Al = 16 and 30; Si/Ga = 63 and 82). Thermogravimetric analysis under hydrogen atmosphere was used as a preliminary screening tool to evaluate the potential of the various catalysts for this application in terms of energy requirements. In addition, batch autoclave reactor experiments (T = 300 °C, PH2 = 20 bar, t = 60 min) were conducted to obtain further information on conversion, product yields and product distribution for the most promising systems. The results show that the catalytic performance in HDPE hydrocracking is determined by a balance between the acidity of the catalyst and its structural accessibility. Accordingly, for catalyst series where the structural and textural properties do not vary with the Si/Al ratio, there is a clear correlation of the HDPE degradation temperature and of the HDPE conversion with the Si/metal ratio (which relates to the acidic properties). In contrast, for catalyst series where the structural and textural properties vary with the Si/Al ratio, no consistent trend is observed and the catalytic performance is determined by a balance between the acidic and textural properties. The product distribution was also found to be influenced by the physical and chemical properties of the catalyst. Catalysts with strong acidity and smaller pores were observed to favor the formation of lighter hydrocarbons. In addition to the textural and acidic properties of the catalyst, the role of coke formation should not be neglected to ensure a comprehensive analysis of the catalytic performance.
- Local induction heating capabilities of zeolites charged with metal and oxide MNPs for application in HDPE hydrocracking: a proof of conceptPublication . Muñoz, Marta; Morales Casero, Irene; Costa, Cátia S.; Multigner, Marta; De La Presa, Patricia; Alonso, Jose M.; Silva, João; Ribeiro, M. Rosário; Torres, Belén; Rams, JoaquinZeolites are widely used in high-temperature oil refining processes such as fluid catalytic cracking (FCC), hydrocracking, and aromatization. Significant energy cost are associated with these processes due to the high temperatures required. The induction heating promoted by magnetic nanoparticles (MNPs) under radio frequency fields could contribute to solving this problem by providing a supplementary amount of heat in a nano-localized way, just at the active centre site where the catalytic process takes place. In this study, the potential of such a complementary route to reducing energetic requirements is evaluated. The catalytic cracking reaction under a hydrogen atmosphere (hydrocracking) applied to the conversion of plastics was taken as an application example. Thus, a commercial zeolite catalyst (H-USY) was impregnated with three different magnetic nanoparticles: nickel (Ni), cobalt (Co), maghemite (γ-Fe2O3 ), and their combinations and subjected to electromagnetic fields. Temperature increases of approximately 80 ◦C were measured for H-USY zeolite impregnated with γ-Fe2O3 and Ni-γ-Fe2O3 due to the heat released under the radio frequency fields. The potential of the resulting MNPs derived catalyst for HDPE (high-density polyethylene) conversion was also evaluated by thermogravimetric analysis (TGA) under hydrogen atmosphere. This study is a proof of concept to show that induction heating could be used in combination with traditional resistive heating as an additional energy supplier, thereby providing an interesting alternative in line with a greener technology.
- 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.