RESUMO
The conversion of waste/by-product materials into efficient sorbents is at the forefront of innovative remediation techniques. In the present study, the relationships among the synthesis conditions, physicochemical properties of synthesized sorbents and Zn2+ and Ni2+ removal efficiencies were studied in detail. Zeolite X, zeolite P, phillipsite, analcime, sodalite and cancrinite were synthesized from industrial perlite by-product material. The zeolite content in the synthesized sorbents and zeolite framework topology (dimensions, numbers and spatial configuration of channels) were the key factors affecting the removal of Zn2+ and Ni2+ from aqueous solutions. Zeolite X-based sorbent exhibited the best sorption performance mainly due to the large zeolite channel dimensions, low Si/Al ratio, high cation exchange capacity and high specific surface area. Nevertheless, the efficiency and stability of this sorbent need to be tested under field conditions prior to its application for remediation technologies.
RESUMO
This paper is focused on the heterogeneously catalyzed transesterification (in a batch reactor) of vegetable oil, including the determination of leached metals. The oil was obtained from the short-season crop Camelina sativa. The reaction was catalyzed by mixed oxides, which were synthesized from Mg/Al hydrotalcites with built-in different types of divalent cations such as Mn, Ca, Co, Ni, and Fe. The various physicochemical properties like the structure by X-ray diffraction, acidity, basicity, and textural properties were measured and the effect of the added cation type on catalyst properties and activity was compared. A noticeable relationship between the cation type and catalytic activity in the transesterification reaction was observed. The highest ester content of 96.6 wt % after 7 h of transesterification was observed for catalysts with nickel and iron. The statistical analysis of results showed that the catalyst activity was mainly influenced by middle-temperature basic sites. The novelty lies in transesterification over five different heterogeneous catalysts-mixed oxides with added divalent metals at the same reaction conditions of C. sativa oil.
RESUMO
The pore characteristics of zeolite samples including two kinds of ZSM-5 crystals as a base case and the unique mono-layered MCM-56 in different structural forms have been studied by the new method QE-TPDA (quasi-equilibrated temperature-programmed desorption and adsorption) in comparison with the standard nitrogen adsorption. Both approaches produce consistent results in terms of micro- and meso-porous features as well as quantitative pore volume values. The benefits of QE-TPDA include fast data acquisition (hours) and small sample size (milligrams). It is very flexible in using various hydrocarbons as probe molecules, which may reveal additional details associated with pores, their internal environment and dimensions/shape of the sorbate molecules. Hence, QE-TPDA is a valuable complementary tool for porosity characterization of the ever increasing diversity of porous materials and their pore structures. This was demonstrated by the results for the desorption of nonane and 2,2-dimethyloctane (DMO). The latter showed an additional maximum in the intermediate temperature range (between 'micro-' and 'mesopore' regions) which could be attributed to adsorption in the subsurface micropores (i.e. the pore mouths) where DMO could be partially adsorbed with t-butyl groups remaining on the outside. This was also reflected in the discrepancy between apparent volumes of micro- and mesopores calculated from the nonane and DMO experiments. Pillared MCM-56 revealed visibly enhanced subsurface micropore adsorption compared to the parent (mono-layer MWW) and MCM-22 (multi-layered MWW) consistent with the expected increase in the content of external 12 ring surface cups.