Search Results (5)

In this research, catalytic cracking of low-density polyethylene (LDPE) has been carried out in the presence of three kinds of typical molecular sieves, including ZSM-5, HY and MCM-41, respectively. The effects of different catalysts on the composition and quantity of pyrolysis products consisting of gas, oil and solid material were systematically investigated and summarized. Specially, the three kinds of catalysts were added into LDPE for pyrolysis to obtain regulatable oil and gas products (H₂, CH₄ and a mixture of C₂–C₄⁺ gaseous hydrocarbons). These catalysts were characterized with BET, NH₃-TPD, SEM and TEM. The results show that the addition of MCM-41 improved the oil yield, indicating that the secondary cracking of intermediate species in primary pyrolysis decreased with the case of the catalyst. The highest selectivity of MCM-41 to liquid oil (78.4% at 650 °C) may be attributed to its moderate total acidity and relatively high BET surface area. The ZSM-5 and HY were found to produce a great amount of gas products (61.4% and 67.1% at 650 °C). In particular, the aromatic yield of oil production reached the maximum (65.9% at 500 °C) when the ZSM-5 was used. Accordingly, with the three kinds of catalysts, a new environment-friendly and efficient recovery approach may be developed to obtain regulatable and valuable products by pyrolysis of LDPE-type plastic wastes. Full article

Catalytic distillation is a technology that combines a heterogeneous catalytic reaction and the separation of reactants and products via distillation in a single reactor/distillation system. This process combines catalysis, kinetics, and mass transfer to obtain more selective products. The heterogeneous catalyst provides the sites for catalytic reactions and the porous surface for liquid/vapor separation. The advantages of catalytic distillation are energy savings, low waste streams, catalyst longevity, higher conversion, and product selectivity; these properties are interesting for petrochemical and petroleum industries. For this study, 100 mL of atmospheric residue of petroleum (ATR) was distilled in the presence of 1.0 g of a micro/mesoporous catalyst composed of a HY-MCM-41, and the reactor used was an OptiDist automatic distillation device, operating according to ASTM D-86 methodology. The products were collected and analyzed by gas chromatography. The samples of ATR, HY/ATR, and HY-MCM-41/ATR were analyzed by thermogravimetry (TG) to determine the activation energies (Ea) relative to the thermal decomposition of the process, using the Ozawa–Flynn–Wall (OFW) kinetic model. The obtained results show a potential catalytic distillation system for use in the reaction of heavy petroleum fractions and product separation from the HY/MCM-41 micro/mesoporous catalyst. The TG data revealed two mass loss events for ATR in the ranges of 100–390 and 390–590 °C, corresponding to volatilization and thermal cracking, respectively. The Ea determined for the thermal degradation of the ATR without a catalyst was in the range of 83–194 kJ/mol, whereas in the presence of the HY-MCM-41 catalyst, it decreased to 61–105 kJ/mol, evidencing the catalytic effect of the micro-mesoporous material. The chromatography analysis allowed for the identification of gasoline and a major production of diesel and gasoil when the HY-MCM-41 mixture was used as the catalyst, evidencing the synergism of the combined effect of the acid sites, the crystalline phase, and the microporosity of the HY zeolite with the accessibility of the hexagonal mesoporous structure of the MCM-41 material. Full article

A low-density polyethylene was hydrocracked to liquid hydrocarbons in autoclave reactors over catalysts containing Pt- and Al-modified MCM-48. Two kinds of Al-modified MCM-48 were synthesized for the reaction: Al-MCM-48 was synthesized using a sol–gel method by mixing Al(iso-OC₃H₇)₃ with Si(OC₂H₅)₄ and surfactant in a basic aqueous solution before hydrothermal synthesis, and Al/MCM-48 was synthesized using a post-modification method by grafting Al³⁺ ions on the surface of calcined Al/MCM-48. X-ray diffraction (XRD) patterns indicated that both Al-MCM-48 and Al/MCM-48 had a cubic mesoporous structure. The Brunauer–Emmett–Teller (BET) surface areas of Al-MCM-48 and Al/MCM-48 were larger than 1000 m²/g. ²⁷Al Magic Angle Spinning-NMR (MAS NMR) indicated that Al³⁺ in Al-MCM-48 was located inside the framework of mesoporous silica, but Al³⁺ in Al/MCM-48 was located outside the framework of mesoporous silica. The results of ammonia temperature-programmed desorption (NH₃-TPD) showed that the acidic strength of various samples was in the order of H-Y > Al/MCM-48 > Al-MCM-48 > MCM-48. After 4 MPa H₂ was charged in the autoclave at room temperature, 1 wt % Pt/Al/MCM-48 catalyst showed a high yield of C₉−C₁₅ jet fuel range hydrocarbons of 85.9% in the hydrocracking of polyethylene at 573 K for 4 h. Compared with the reaction results of Pt/Al/MCM-48, the yield of light hydrocarbons (C₁−C₈) increased over Pt/H-Y, and the yield of heavy hydrocarbons (C₁₆−C₂₁) increased over Pt/Al-MCM-48 in the hydrocracking of polyethylene. The yield of C₉−C₁₅ jet fuel range hydrocarbons over the used catalyst did not decrease compared to the fresh catalyst in the hydrocracking of polyethylene to jet fuel range hydrocarbons over Pt/Al/MCM-48. Full article

Clofazimine (CLZ) is an effective antibiotic used against a wide spectrum of Gram-positive bacteria and leprosy. One of its main drawbacks is its poor solubility in water. Silica based materials are used as drug delivery carriers that can increase the solubility of different hydrophobic drugs. Here, we studied how the properties of the silica framework of the mesoporous materials SBA-15, MCM-41, Al-MCM-41, and zeolites NaX, NaY, and HY affect the loading, stability, and distribution of encapsulated CLZ. Time-correlated single-photon counting (TCSPC) and fluorescence lifetime imaging microscopy (FLIM) experiments show the presence of neutral and protonated CLZ (1.3–3.8 ns) and weakly interacting aggregates (0.4–0.9 ns), along with H- and J-type aggregates (<0.1 ns). For the mesoporous and HY zeolite composites, the relative contribution to the overall emission spectra from H-type aggregates is low (<10%), while for the J-type aggregates it becomes higher (~30%). For NaX and NaY the former increased whereas the latter decreased. Although the CLZ@mesoporous composites show higher loading compared to the CLZ@zeolites ones, the behavior of CLZ is not uniform and its dynamics are more heterogeneous across different single mesoporous particles. These results may have implication in the design of silica-based drug carriers for better loading and release mechanisms of hydrophobic drugs. Full article

Micro- and mesoporous silica-based materials are a class of porous supports that can encapsulate different guest molecules. The formation of these hybrid complexes can be associated with significant alteration of the physico-chemical properties of the guests. Here, we report on a photodynamical study of a push–pull molecule, trans-4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM), entrapped within faujasite-type zeolites (HY, NaX, and NaY) and MCM-41 in dichloromethane suspensions. The complex formation gives rise to caged monomers and H- and J-aggregates. Steady-state experiments show that the nanoconfinement provokes net blue shifts of both the absorption and emission spectra, which arise from preferential formation of H-aggregates concomitant with a distortion and/or protonation of the DCM structure. The photodynamics of the hybrid complexes are investigated by nano- to picosecond time-resolved emission experiments. The obtained fluorescence lifetimes are 65–99 ps and 350–400 ps for H- and J-aggregates, respectively, while those of monomers are 2.46–3.87 ns. Evidences for the presence of a charge-transfer (CT) process in trapped DCM molecules (monomers and/or aggregates) are observed. The obtained results are of interest in the interpretation of electron-transfer processes, twisting motions of analogues push–pull systems in confined media and understanding photocatalytic mechanisms using this type of host materials. Full article