Authors:V. Rac, Vesna Rakić, S Gajinov, Vera Dondur, and Aline Auroux
In this work, room temperature interaction of n-hexane with HZSM-5 (Si/Al=20) and ion-exchanged
samples containing one (CuZSM-5, FeZSM-5 and MnZSM-5) or two transition-metal
cations (Fe,CuZSM-5; Cu,MnZSM-5 and Fe,MnZSM-5) was studied by microcalorimetry
and TPD methods. Both differential heats and the amounts of n-hexane
adsorbed per one unit cell were quantitatively determined. Higher heats of
adsorption and higher amounts of adsorbed gas were found for ion-exchanged
samples than for HZSM-5. The experiments of n-hexane
adsorption on hydrated samples were also performed. The amounts of n-hexane
adsorbed on hydrated ZSM-5 were lower in comparison with dehydrated samples,
while the energies of interaction were similar.
Authors:Angela Martins, João M. Silva, Fernando Râmoa Ribeiro, and M. Filipa Ribeiro
-22 are less explored [ 17 ]. Previously, we reported preliminary studies regarding the potentialities of MCM-22 zeolite in n -hexane transformation [ 7 , 18 ]. This work presents a more detailed study regarding n -hexane transformation used as a
Authors:Bianca V. Sousa, Karoline D. Brito, José J. N. Alves, Meiry G. F. Rodrigues, Carlos M. N. Yoshioka, and Dilson Cardoso
isomerization of n -paraffin fractions. As a result, the need to maintain high octane number fuel has recently attracted much interest in the isomerization processes involving alkanes, particularly linear alkanes such as n -hexane and n -heptane with octane
]. Accordingly, there is a pressing need for new, inexpensive and highly selective reusable catalysts for the oxidation of alkanes.
Recently bimetallic Co–Mg oxide silica supported catalysts were found to promote complete oxidation of n -hexane to CO 2
desorption coupled with mass spectrometer as a detector (TPD), IR and 13C
NMR measurements are used to study the adsorption of n-hexane
on hydrated HZSM-5 and NH4ZSM-5 zeolites. The 13C
NMR measurements show that n-hexane can
access the pore structure of ZSM-5 zeolites previously saturated with water.
TPD spectra of n-hexane are monitored in
the temperature region 50–300C, in the case of fully or partially
hydrated samples; two-stage desorption of n-hexane
is found. Simultaneous desorption of water and n-hexane
in the same temperature region are found, in all investigated samples.
The origin of kinks (steps) on sorption isotherms was examined for the sorption of benzene and n-hexane on silicalite-1. In
both cases sorption revealed the existence of two different binding sites. There was no equilibrium (or a very slow one),
between molecules bound at different sites. Sorption energies within particular centres display more or less wide overlapping
distributions leading to a single resultant isotherm. Depending on differences in binding energies and degree of overlapping,
the resulting isotherms exhibit steps (benzene) or no steps (n-hexane).
In fact, the sorption isotherm of benzene being a sum of two elemental isotherms (Ω1 and Ω2) of different shapes is characterized by a ‘kink’, in contrast to n-hexane the elemental isotherms of which are of the same
Authors:Bharat Modhera, Mousumi Chakraborty, Hari Bajaj, and Parimal Parikh
Hydroisomerization of n-hexane simultaneously proceeding with benzene saturation over platinum impregnated nano-crystalline zeolite beta (Si/Al = 25)
at 1.0 MPa and 573–673 K was studied. The feed contained 30 wt% benzene. The synthesized catalyst was characterized by various
techniques, e.g., powder X-ray diffraction, IR spectroscopy, thermal analysis, scanning electron microscopy and nitrogen adsorption.
At the operating conditions used, total saturation of benzene with 95% selectivity to cyclohexane (CH) and methylcyclopentane
(MCP) was observed. n-Hexane conversion increased with temperature whether benzene was present or not during the reaction. However, in the presence
of benzene, n-hexane conversions as well as isomer selectivities were observed to be lower. This was attributed to reduced availability
of acid sites by predominating benzene adsorption. Formation of carbenium ion on an acid site is questioned and plausible
mechanism has been suggested.
The isotherms of adsorption-desorption of the vapour of benzene, cyclohexene and n-hexane on different porous silica gels
were measured gravimetrically. For all the adsorbates, the amount of vapour condensed in the adsorbent pores is significantly
greater than the amount adsorbed. The isotherms of all the adsorbates are linear in a wide range of relative pressures.
Equilibrated thermodesorption (TPED) and quasi-equilibrated temperature programmed desorption and adsorption (QE-TPDA) were
employed as methods for studying the influence of different extraframework cations (Na+, K+, Li+, Cu2+, Zn2+, or Mg2+) on adsorption of n-hexane on ZSM-5 zeolite with high Al content (Si/Al = 15). Considerable influence of the cations on both
initial adsorption in the micropores and ordering of the adsorbed molecules, occurring at high coverages, has been observed.
This influence is reflected by the values of the adsorption enthalpy and entropy, determined by fitting the dual site Langmuir
(DSL) adsorption function to the equilibrated thermodesorption profiles. However, no clear correlation between the determined
parameters and properties of the extraframework cations could be found.
Authors:V. Jedináková, P. Vaňura, J. Žilková, V. Bílek, and F. Touati
The synergistic solvent extraction of Eu(III) and some other rare earth elements from nitrate solutions (HNO3+LiNO3) by a mixture of (TBP+D2EHPA) in n-hexane and cyclohexane has been investigated at 22 °C. Antagonism found in europium extraction from 0.1M HNO3 transforms into a synergistic effect. The synergistic effects existing for all investigated metals in extraction from 0.1M HNO3+3M LiNO3 were caused by formation of mixed complexes of the type Ln(D2EHPA)2nH2n–3+1(NO3)1TBPm, where 1=1 or 2. The selectivity of the extraction in a synergistic system is lower for the La–Yb pair than in the case of D2EHPA extraction under the same conditions. On the other hand, the application of the synergistic mixture is more suitable for Eu–Ho separation. Thus the synergistic effect can be used for the separation or refining of some lanthanides.