Gas-expanded liquids for sustainable catalysis and novel materials: Recent advances

Employing a multiscale systems-based research approach, chemists and chemical engineers at the Center for Environmentally Beneficial Catalysis (CEBC) are collaboratively addressing major grand challenges facing the sustainable manufacture of fuels and chemicals from both traditional and renewable feedstocks. By judiciously combining the principles of green chemistry and green reactor engineering, augmented by valuable insights from industrial partners, CEBC researchers are developing alternative technology concepts that minimize the environmental footprint of chemical manufacturing processes including the reduction of carbon emissions. Such collaborations have resulted in several remarkable discoveries as follows: CO₂-expanded liquids (CXLs) as reaction media for selective and inherently safe O₂ oxidations including that for terephthalic acid production from p-xylene with potentially reduced solvent burning (i.e., reduced carbon footprint); propylene oxide production with environmentally benign solvents and oxidant, exploiting the compressibility of propylene at ambient temperatures for process intensification; a novel pressure-intensified ethylene oxide process virtually eliminating CO₂ formation as a byproduct; highly selective hydroformylation of higher olefins employing CXLs and soluble polymer-supported homogeneous Rh-based catalysts that are easily retained in solution while the product is isolated by membrane filtration; and creation of nanoparticles of transition metal complexes with unique functional properties such as reversible oxygen binding and room-temperature nitric oxide disproportionation. Quantitative economic and environmental impact analyses have been employed to benchmark CEBC's novel technology concepts against conventional processes and to guide research and development. Examples of such advances in green processing are discussed in this review.     

X-ray, scanning electron microscopy and electrical properties of synthetic fresnoite (Ba2TiSi2O8) ceramics

Polycrystalline ceramic samples of fresnoite (Ba₂TiSi₂O₈ or BTS) have been prepared by a standard solid-state reaction method using high-purity oxides and carbonates. For one set of compounds, in stoichiometric ratio BaCO₃, TiO₂ and SiO₂ were melted at 1300°C and then sintered into pellet form, whereas the other set of compounds have been prepared without melting and sintered into pellet form at 1250°C. The formation of the single-phase compound and its structural parameters were investigated by X-ray diffraction followed by Rietveld refinement and scanning electron microscopic (SEM) techniques. A better agreement between the observed and calculated X-ray diffraction patterns was obtained by performing the Rietveld refinement with a structural model using the non-centrosymmetric space group P4bm. A better agreement between observed and calculated d-values shows that the lattice parameters calculated using the Rietveld refinement analysis are better than that of the earlier report so far. The activation energies of both compounds were calculated by measuring its dc electrical conductivities. The results are discussed in detail.     

Characterization of calcium containing plasma electrolytic oxidation coatings on AM50 magnesium alloy

An attempt was made to produce calcium containing plasma electrolytic oxidation (PEO) coatings on AM50 magnesium alloy using an alkaline electrolyte. This study was performed in three alkaline electrolytes containing calcium hydroxide and sodium phosphate with three different mass ratios viz., 1:2.5, 1:5 and 1:7.5. All the three coatings produced were found to contain Ca and P in appreciable amounts. The concentration of P was found to be higher in the coatings obtained in the electrolytes with higher concentration of phosphate ions. Even though all the three coatings were found to be constituted with magnesium oxide and magnesium phosphate phases, X-ray diffraction analyses revealed that the phase composition was influenced by the phosphate ion concentration/conductivity of the electrolyte. Further, the PEO coating obtained in the 1:7.5 ratio electrolyte was found to contain di-calcium phosphate (monetite) and calcium peroxide phases, which were absent in the other two coatings. Potentiodynamic polarization studies performed in 0.1 M NaCl solution showed that the coatings obtained from the 1:5 ratio electrolyte possessed a superior corrosion resistance, which is attributed to the combined effect of thickness, compactness and phase/chemical composition of this coating.     

Quadruply hydrogen bonded cytosine modules for supramolecular applications

In view of the range of properties required from supramolecular materials, there is clearly a need for new strong quadruple hydrogen bonded modules, which can be used in polymer or copolymer synthesis via the self- or hetero-association of complimentary units. A cytosine-based module has been prepared for supramolecular applications using a straightforward synthetic approach. The cytosine module was designed such that it does not undergo tautomeric changes observed with ureidopyrimidinones. The cytosine module was capable of forming quadruple hydrogen bonded assemblies both in solution and in the solid state, and the structure of the dimeric self-assembled unit was confirmed by single-crystal X-ray and solution NMR techniques. The dimerization constant was estimated to be greater than 9 x 106 M-1 in deuterated benzene. The capacity of the cytosine-based module to strongly hetero-associate with the ureidopyrimidinone module was demonstrated, and a supramolecular polymer of a bifunctional unit incorporating the cytosine module and PEG-based linker was described.     

Ternary semigroups

A ternary semigroup is a nonempty set together with a ternary multiplication which is associative. Analogous to the theory of semigroups, a regularity condition on a ternary semigroup is introduced and the properties of regular ternary semigroups are studied. Associated with a ternary semigroup, a semigroup called the semigroup cover is constructed and its properties are investigated.     

Applications of quantum-classical and quantum-stochastic molecular dynamics simulations for proton transfer processes

Quantum-classical and quantum-stochastic molecular dynamics models (QCMD/QSMD) are formulated and applied to describe proton transfer processes in three model systems - the proton bound ammonia-ammonia dimer in an external electrostatic field; malonaldehyde, which undergoes a quantum tautomeric rearrangement; and phospholipase A₂, an enzyme which induces a water dissociation process in its active site followed by proton hopping to a histidine imidazole ring. The proton dynamics are described by the time-dependent Schrödinger equation. The dynamics of the classical atoms are described using classical molecular dynamics. Coupling between the quantum proton (s) and the classical atoms is accomplished via conventional or extended Hellmann-Feynman forces, as well as the time-dependence of the potential energy function in the Schrödinger equation. The interaction of the system with its environment is described by stochastic forces. Possible extensions of the models as well as future applications in molecular structure and dynamics analysis will be briefly discussed.     

On the Fourier coefficients of contracted functions

РАБОтА пОсВьЩЕНА ИжУ ЧЕНИУ сВьжИ кОЁФФИцИ ЕНтОВ ФУРьЕ ФУНкцИИ ?(x) И g(x) тАкИх ЧтО (1) $$\parallel \Delta _h^m g(x)\parallel _{L^2 } \leqq \parallel \Delta _h^m f(x)\parallel _{L^2 } $$ Дль ВськОгОh≧0 И НЕкОт ОРОгОт. пОкАжАНО, ЧтО сУЩЕстВ УУт НЕпРЕРыВНыЕ ФУНк цИь ?(x) Иg(x), УДОВлЕтВОРьУЩИЕ сОО т-НОшЕНИУ (1), И тАкИЕ, ЧтО $$\mathop \sum \limits_{n = 0}^\infty [a_n^2 (f) + b_n^2 (f)]^{\alpha /2}< \infty $$ Дль ВськОгО α>0 И $$\mathop \sum \limits_{n = 0}^\infty [a_n^2 (g) + b_n^2 (g)]^{\beta /2} = \infty $$ Дль ВськОгОΒ<2. АНАлОгИЧНыИ РЕжУльт Ат ДОкАжыВАЕтсь И Дль пЕРИОДИЧЕскИх МУльт ИплИкАтИВНых ОР-тОНО РМИРОВАННых сИстЕМ.     

Volumetric and acoustic studies of aqueous l-arginine·HCl and l-proline in electrolytic and non-electrolytic solutions at various temperatures

Densities and speed of sound of l-arginine hydrochloride and l-proline within the concentration range (0.03–0.2) mol.kg^?1 in water and in aqueous NaCl and Urea are determined between temperatures 288.15 K and 318.15 K and at one atmospheric pressure. Densities and speeds of sound have been used to calculate apparent molar volume of solute ($V_{\phi }$), isentropic compressibility of solution (${\kappa }_S$), apparent molar isentropic compressibility ($K_{S,\phi }$) of solute, limiting apparent molar volume ($V_{\phi }^0$), limiting apparent molar volume of transfer (${\Delta }_{tr}{V}_{\phi }^0$), limiting apparent molar expansibility ($E_{\phi }^0$), limiting apparent molar isentropic compressibility ($K_{S,\phi }^0$) and limiting apparent molar isentropic compressibility of transfer (${\Delta }_{tr}{K}_{S,\phi }^0$). These results are then interpreted in terms of intermolecular interactions. The concentration dependencies of the calculated quantities, their limiting values and temperature characteristics are discussed in terms of solute - solvent and solute - solute interactions at experimental conditions.     

The NADH Electrochemical Detection Performed at Carbon Nanofibers Modified Glassy Carbon Electrode

In this work, the capability of carbon nanofibers to be used for the design of catalytic electrochemical biosensors is demonstrated. The direct electrochemistry of NADH was studied at a glassy carbon electrode modified using carbon nanofibers. A decrease of the oxidation potential of NADH by more than 300 mV is observed in the case of the assembled carbon nanofiber‐glassy carbon electrode comparing with a bare glassy carbon electrode. The carbon nanofiber‐modified electrode exhibited a wide linear response range of 3×10^?5 to 2.1×10^?3 mol L^?1 with a correlation coefficient of 0.997 for the detection of NADH, a high specific sensitivity of 3637.65 (μA/M cm²), a low detection of limit (LOD=3σ) of 11 μM, and a fast response time (3 s). These results have confirmed the fact that the carbon nanofibers represent a promising material to assemble electrochemical sensors and biosensors.     

Development of continuous surfactin production from potato process effluent by Bacillus subtilis in an airlift reactor

The biosurfactant surfactin has the potential to aid in the recovery of subsurface organic contaminants (environmental remediation) or crude oils (oil recovery). However, high medium and purification costs limit its use in these high-volume applications. In previous work, we showed that surfactin can be produced from an inexpensive low-solids (LS) potato process effluent with minimal amendments or pretreatments. Previous research has also shown that 95% or more of the surfactin in Bacillus subtilis cultures can be recovered by foam fractionation. In this work, we present the results of research to integrate surfactin production with foam fractionation. Experiments were performed in an airlift reactor, with continuous collection of the foam through a tube at the top of the column. Preliminary results using both purified potato starch and unamended low-solids potato process effluent as substrates for surfactin production indicate that the process is oxygen limited and that recalcitrant indigenous bacteria in the potato process effluent may hamper continuous surfactin production.