Molecularly
imprinted polymers (MIPs) were prepared by the precipitation
polymerization process, with vitamin E as the template molecule, ethylene
glycol dimethacrylate as the cross-linker, and three different functional
monomers, respectively. Adsorption experiments were conducted to investigate
the performance of each MIP and compared to the nonimprinted polymers
(NIPs). It was found that MIPs are superior to NIPs in general, with
acrylamide-based MIP showing the best adsorption capacity of 38.8
mg·g–1 and an imprinting factor of 2.6. The
optimal imprinting ratio and cross-linking ratio to be 1:5 and 5:1,
respectively. The Freundlich equation was found superior to Langmuir
to describe the adsorption isotherm data on the MIP/NIP. The adsorption
of vitamin E on the MIP was found to be a heterogeneous process and
consists of two mechanisms, which were confirmed by the analysis of
the thermodynamic properties of the adsorption process.
Ethylene is an important feedstock for the production
of many key-valued
compounds, especially polymers. About 60% of the total ethylene produced
is utilized for the production of polyethylene, while ethylene is
normally produced by steam cracking of naphtha along with traces of
ethane, which is undesirable. Considering the energy-intensive nature
of the current technology to obtain ultrapure ethylene, the development
of novel materials for separating ethylene from ethane by adsorption
is of great significance, yet it remains challenging owing to the
close molecular sizes and physical properties of the two compounds.
Both ethylene- and ethane-selective adsorbents are reviewed in this
work. Yet, as the industrial feed is rich in ethylene with traces
of ethane, in order to obtain polymer grade ethylene, multiple adsorption–desorption
cycles are required, which is yet again energy-demanding. Thus, ethane-selective
adsorbents are energetically favorable; hence, in this Review, we
pay particular focus on ethane-selective adsorbents. The rationale
behind reverse-selective adsorbents is critically reviewed and discussed.
Most of the ethane-selective adsorbents have been reported to exhibit
low selectivity compared to ethylene-selective ones, as reverse-selectivity
is mostly based on weak van der Waals interactions. In addition, we
focused on various reported mechanisms behind the adsorptive separation
of ethane/ethylene mixtures, as well as modifications and surface
functionalization techniques reported for different types of adsorbents
investigated for this separation.
A molecularly imprinted polymer (MIP) was synthesized via a two-step swelling polymerization method for the purification of lincomycin. Polystyrene microspheres were prepared by the dispersion-polymerization process and used as the substrate. Methacrylic acid was used as the functional monomer, whereas ethylene glycol dimethacrylate was the cross-linker. The MIP was structurally characterized and examined for its separation performance at different conditions (temperature, solvents, etc.). It was found that the MIP possesses the good sphericity, porosity, monodispersity, and a high adsorption capacity of (180 μmol/g) in chloroform solution. Comparison studies showed that the MIP presents a higher capacity than the NIP (non-imprinted polymer) in chloroform solution and a much higher capacity in the practical lincomycin fermentation solution extracts, confirming the underlining mechanisms of the MIP. Scatchard plot revealed two adsorption mechanisms on the MIP, whereas the isotherm is better described by Freundlich equation. The adsorption/elution kinetics demonstrated that the MIP possesses good elution/regeneration capabilities with the elution ratio > 93%.
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