Theoretical analysis of inhibition effect on steady states of enzymatic membrane reactor with substrate and product retention for reaction producing weak acid

The aim of this study is to formulate a model of enzymatic membrane reactor (EMR), i.e., a continuous, stirred tank bioreactor with full enzyme recycle, for a reaction producing a weak acid, and to explore the effect of substrate and product inhibition of different mechanisms coupled with transport properties of the membrane on the static behaviour of the system. The inhibition of an enzyme by a substrate leads to the non-monotonicity of reaction rate expression with respect to the substrate concentration. If a product of enzymatic reaction, taking place in the EMR, influences the pH of a reaction mixture this is also the factor causing the non-monotonicity of the substrate and product dependent reaction rate. The character of these dependencies affects substantially the structure of the steady states of the reactor. The bifurcation diagrams, shown in the work, are of different characters depending on the bifurcation parameter. It has been found, that bifurcation diagrams for competitive and uncompetitive inhibition by a substrate differ in the number and position of bifurcation points. Steady states of multiplicity five have been localised in case of uncompetitive inhibition by the substrate at high affinity of the enzyme to this substrate. Retention of reagents, related to transport properties of a membrane, influences significantly the effectiveness of a process. A specially written software in Delphi™ has been used for the calculations.     

Synthesis and emission analysis of RE (Eu or Dy):Li2TiO3 ceramics

The development and photoluminescence analysis of Eu³⁺or Dy³⁺ ions in the matrix of lithium titanate (Li₂TiO₃) ceramics by using a solid state reaction method are reported. Emission spectra of Eu³⁺:Li₂TiO₃ ceramics have shown strong red emission at 611 nm (⁵D₀ → ⁷F₂) with λ_exci = 392 nm (⁷F₀ → ⁵L₆) and from the Dy³⁺:Li₂TiO₃, a blue emission at 493 nm (⁴F_9/2 → ⁶H_15/2) and also an yellow emission at 582 nm (⁴F_9/2 → ⁶H_13/2) have been observed with λ_exci = 366 nm (⁶H_15/2 → ⁶P_5/2). Both the rare-earth ions containing ceramics have displayed their brighter emission performance from their measured spectral results. In addition, X-ray diffraction (XRD), Fourier transform infra red (FTIR) spectroscopy, scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX) have been used to characterize the structural properties of (Eu³⁺ or Dy³⁺):Li₂TiO₃ ceramics.     

Investigation of the stress and strain state of clay pipes under fire condition

The focus of this paper is given to investigating the testing and evaluation method of stress and deformation behaviour of clay pipe elements like chimneys under cyclic high temperature. The experimental study on the temperature–time curves and on the radial deformation–temperature curves of a series of fire-resistant clay pipes was carried out. The tensile strength and the compressive strength, the elastic modulus before and after fire, the stress and deformation properties and the cracking behaviour of the clay pipes under fire conditions have been analyzed. The theoretical analysis corresponds well with the experimental results and tends to prove that the elastic deformation can be the most significant component in fixed-end clay pipes. This study is useful for evaluation of the stress–strain properties of ceramic pipes and provides a beneficial test method for the pipe member in small-scale or in full-scale tests under fire temperatures.     

Magnetic and thermal expansion properties of chromium-substituted lithium ferrite

The structure, magnetic, and thermal expansion properties of chromium-substituted lithium ferrite have been investigated. The lattice constant (Å) decreases linearly as a (x) = 8.32366 − 0.04338x for Li_0.5Fe_2.5−xCr_xO₄ (x = 0.0–1.0). When increasing Cr content, the initial permeability decreased gradually. The average thermal expansion coefficient of Li_0.5Fe_2.5−xCr_xO₄ (x = 0.0–1.0) varied from 15.34 to 17.77 ppm/°C, with increasing Cr content, the average thermal expansion coefficient decreased. The average thermal expansion coefficient (ppm/°C) in the range of 25–850 °C give the polynomial correlation as follows, TEC (x) = 1 7.775 − 0.216x − 0.723x² − 1.493x³ for Li_0.5Fe_2.5−xCr_xO₄ (x = 0.0–1.0).     

Structure and electrical properties of Nd2O3-doped 0.82Bi0.5Na0.5TiO3–0.18Bi0.5K0.5TiO3 ceramics

Nd₂O₃ doped 0.82Bi_0.5Na_0.5TiO₃–0.18Bi_0.5K_0.5TiO₃ (abbreviated to BNKT) binary lead-free piezoelectric ceramics were synthesized by the conventional mixed-oxide method. The results show that the BNKT ceramics with 0–0.15 wt.% Nd₂O₃ doping possesses a single perovskite phase with rhombohedral structure. The grain size of BNKT decreased with the addition of Nd₂O₃ dopant. The temperature dependence of the dielectric constant ?_r revealed that there were two-phase transitions from ferroelectric to anti-ferroelectric and anti-ferroelectric to paraelectric. A diffuse character was proved by linear fitting of the modified Curie–Weiss law. At room temperature, the specimens containing 0.0125 wt.% Nd₂O₃ with homogeneous microstructure presented excellent electrical properties: the piezoelectric constant d₃₃ = 134 pC/N, the electromechanical coupling factor K_p = 0.27, and the dielectric constant ?_r = 925 (1 kHz).     

THE MODIFIED PGR EQUATION OF STATE: ASYMMETRIC MIXTURE VLE REPRESENTATIONS AND PREDICTIONS

A set of mixing rules was proposed for the modified Park-Gasem-Robinson (PGR) equation of state (EOS) to extend its predictions to mixtures. The phase behavior predictive capability of this segment-segment interaction model was evaluated for selected binary asymmetric mixtures involving ethane, carbon dioxide, and hydrogen in normal paraffins. The predicted bubble point pressures for the ethane + n-paraffin and carbon dioxide + n-paraffin binaries were compared to those of the Peng-Robinson (PR), simplified perturbed hard-chain theory (SPHCT), and original PGR equations. The a priori predictive capability of the modified PGR EOS is significantly better than that of the PR, SPHCT, and original PGR equations of state for ethane binaries with absolute-average percent deviation (%AAD) of 5%. However, this EOS produces comparable representations for ethane binaries (%AAD of 1.9%) and carbon dioxide binaries (%AAD of 2.0). For hydrogen binaries, the modified PGR EOS showed much better representations (%AAD of 1.7) than the original PGR equation and was comparable to the PR equation.     

高分子材料的老化研究进展

介绍了有关高分子材料在环境因素作用下老化研究的历史,综述了橡胶、塑料及胶粘剂的环境老化行为、国内外研究的发展及现状,展望了高分子材料老化的研究动向和发展趋势.     

Thermal properties and morphology of recycled poly(ethylene terephthalate)/maleic anhydride grafted linear low‐density polyethylene blends

Properties of recycled Poly(ethylene terephthalate) were greatly improved. Recycled PET was blended with LLDPE‐g‐MA by low‐temperature solid‐state extrusion. Mechanical properties of the blends were affected obviously by the added LLDPE‐g‐MA. Elongation at break reaches 352.8% when the blend contains 10 wt % LLDPE‐g‐MA. Crystallization behavior of PET phase was affected by LLDPE‐g‐MA content. Crystallinity of PET decreased with the increase of LLDPE‐g‐MA content. FTIR testified that maleic anhydride group in LLDPE‐g‐MA reacted with the end hydroxyl groups of PET and PET‐co‐LLDPE‐g‐MA copolymers were in situ synthesized. SEM micrographs display that LLDPE‐g‐MA phase and PET phase are incompatible and the compatibility of the blends can be improved by the forming of PET‐co‐LLDPE‐g‐MA copolymer. LLDPE‐g‐MA content was less, the LLDPE‐g‐MA phase dispersed in PET matrix fine. With the increase of LLDPE‐g‐MA content, the morphology of dispersed LLDPE‐g‐MA phase changed from spherule to cigar bar, then to irregular spherule. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis and properties of polyolefin graft copolymers by a grafting “onto” reactive process

The synthesis of graft copolymers by the grafting “onto” process in the molten state was described. Functional oligomers obtained by telomerization or by ATRP were reacted onto maleic anhydride grafted polypropylene (PP-g-MAH) and poly(ethylene-ter-maleic anhydride-ter-methyl acrylate) (P(E-ter-MAH-ter-MeA)) to obtain PP-g-PMMA and P(E-ter-MAH-ter-MeA)-g-PMMA graft copolymers, respectively. The grafting of different mono-functional oligomers bearing hydroxyl, aliphatic amine or aromatic amine functions was investigated at 180 °C and at 200 °C. The grafting efficiency was very low in the case of hydroxyl-terminated PMMA, while the amine-terminated PMMA led to high yields. In the last part, PP-g-PMMA and P(E-ter-MAH-ter-MeA)-g-PMMA graft copolymers were synthesized by the reaction of aliphatic amine functional PMMA oligomers onto PP-g-MAH and P(E-ter-MAH-ter-MeA), respectively. The influence of the molecular weight of PMMA oligomers was investigated and showed that he grafting efficiency slightly decreases with the increasing molecular weight. However, this process allows the synthesis of PP-g-PMMA graft copolymers containing 6-45 wt% of PMMA side chains. The microstructure of the nanostructured PP-g-PMMA and P(E-ter-MAH-ter-MeA)-g-PMMA graft copolymers was investigated by TEM and SEM. This was established that the addition of PP-g-PMMA in PP/PMMA binary blends allows to control their morphologies and stabilities.     

Structure and surface elemental state analysis of polyimide resin film after carbonization and graphitization

The carbon materials prepared from polyimide (PI) resin film were investigated by TG‐DTG, X‐ray powder diffraction (XRD), and X‐ray photoelectron spectroscopy (XPS) analysis. TG‐DTG study revealed that the weight loss of PI resin film during carbonization occurred in three stages, and the most serious changes occurred at 605.5°C. XRD results indicated that a disorder structure occurred after the carbonization at 600°C and graphite crystallite appeared gradually with increasing the temperature. And PI resin film still presented some characteristics of nongraphitizing carbon, after graphitizing at 2600°C. XPS analysis identified that pyrrole type nitrogen was a main component of surface nitrogen atoms after carbonization. When the temperature reached 2600°C, nitrogen atoms disappeared totally; the reason why oxygen atoms still existed in the material at so high temperature was our subject of interesting matter in the later study. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008