Amir Vahid

Removal of H2S from crude oil via stripping followed by adsorption using ZnO/MCM-41 and optimization of parameters

In the present work, H2S of crude oil was removed via a two-step method including stripping followed by adsorption. First, ZnO/MCM-41 adsorbents containing 5, 17.5 and 30 wt% of zinc were synthesized and characterized using XRD and nitrogen physisorption. Then, these materials were used as adsorbents for the removal of the H2S stripped from crude oil. At second step, the H2S of crude oil was extracted to gas phase by hot stripping. The obtained extract was collected in a storage tank for the subsequent H2S adsorption process. A three-factor Box–Behnken design with five center points and one response was performed for the optimization of adsorption of H2S. The influence of process parameters and their interactional effects on the adsorption of H2S were analyzed using the obtained adsorption experimental data. A model including three important factors, i.e., temperature, space velocity and amount of supported zinc and their interactions, was developed to generate the optimum condition. The point of Znxa0=xa030 wt%, Txa0=xa0300xa0°C and space velocityxa0=xa03,000xa0h−1 had the optimum point with the highest break point time (tbpxa0=xa0973xa0min).

On-line micro column preconcentration system based on amino bimodal mesoporous silica nanoparticles as a novel adsorbent for removal and speciation of chromium (III, VI) in environmental samples.

BackgroundChromium (VI) has toxic and carcinogenic effects. So, determination and speciation of chromium in environmental samples is very important in view of health hazards. In this study, solid phase extraction (SPE) based on bulky amine-functionalized bimodal mesoporous silica nanoparticles (NH2-UVM-7) as a novel nanoadsorbent was applied for preconcentration and speciation of chromium (III, VI) in water samples.MethodsUVM-7 was synthesized via atrane route and subsequently functionalized with amino silane via grafting method. In SPE procedure, polymer tubing as a micro-column was filled with NH2-UVM-7 adsorbent. Preconcentration and speciation of Cr (III) and Cr (VI) ions with NH2-UVM-7 were obtained in water samples due to the fact that only Cr (VI) ions can be complexed with-NH2 groups at optimized pH. Finally, chromium concentration was determined by flame atomic absorption spectrometry (F-AAS).ResultsTEM, XRD, and SEM results confirmed the beneficial properties of NH2-UVM-7 as the adsorbent for chromium extraction. Under the optimal conditions, linear calibration curve, detection limit and preconcentration factor were obtained 6–320xa0μg/ L, 1.2xa0μg/L and 66.7, respectively (RSDu2009<u20095xa0%). The efficiency of nanoadsorbent for preconcentration and extraction of Cr (VI) was 96xa0%, whereas it was less than 5xa0% for Cr (III).ConclusionsThe developed NH2-UVM7-based SPE/F-AAS method has enough sensitively and simplicity for speciation and determination of Cr (VI) and Cr (III) ions in real water samples. Good recoveries, with low detection limits and good preconcentration factors are the main advantages of this procedure.

Effect of the structure of the support and the aminosilane type on the adsorption of H2S from model gas

In the present work, three different porous supports, i.e. MCM-41, SBA-15 and UVM-7 were synthesized and functionalized with three different aminosilanes (C9H23NO3Si, C8H22N2O3Si and C10H27N3O3Si). All the synthesized samples were characterized using XRD, nitrogen physisorption, elemental analysis and acid–base titration, SEM and TEM. The obtained results revealed that all the samples have a well-ordered structure and amine groups were successfully grafted on their pore surfaces. Then, the ability of amine-functionalized samples to adsorb H2S was investigated. In the case of MCM-41, changing the aminosilane functional group did not change tbp (the time at which the outlet concentration of H2S reaches its maximum admissible value in the effluent). SBA-15 functionalized with C8H22N2O3Si showed enhanced tbp in comparison with C9H23NO3Si, but C10H27N3O3Si showed very low tbp (even lower than C9H23NO3Si) which might be attributed to pore blocking originating from the very large size of C10H27N3O3Si. UVM-7 had the highest tbp for all three of the aminosilane functional groups. This might be attributed to the very large pore size of UVM-7 with respect to those of SBA-15 and MCM-41. In addition, nanosize particles of UVM-7 facilitate the adsorption of H2S for this type of adsorbent, which should be due to the unconstrained diffusion of H2S within the mesopores of UVM-7. The efficiency of an aminosilane functional group strongly depends on the pore size of the support rather than its surface area.

Multilevel morphology of complex nanoporous materials

This work exploits gas adsorption and small-angle X-ray scattering (SAXS) to determine the morphology of complex nanoporous materials. We resolve multiple classes of porosity including previously undetected large-scale texture that significantly compromises the canonical interpretation of gas adsorption. Specifically, a UVM-7 class mesoporous silica was synthesized that has morphological features on three length scales: macropores due to packing of 150 nm globules, 1.9 nm radius spherical mesopores inside the globules, and >7 nm pockets on and between the globules. The total and external surface areas, as well as the mesopore volume, were determined using gas adsorption (αs-plot) and SAXS. A new approach was applied to the SAXS data using multilevel fitting to determine the surface areas on multiple length scales. The SAXS analysis code is applicable to any two-phase system and is freely available to the public. The total surface area determined by SAXS was 12% greater than that obtained by gas adsorption. The macropore interfacial area, however, is only 30% of the external surface area determined by the αs-plot. The overestimation of the external surface area by the αs-plot method is attributed to capillary condensation in nanoscale surface irregularities. The discrepancy is resolved assuming that the macropore-globule interfaces harbor fractally distributed nooks and crannies, which lead to gas adsorption at pressures above the mesopore filling pressure.