Shortcut method for evaluation and design of a hybrid process for enantioseparations

Hybrid processes for enantioseparations have a considerable potential for reducing investment and operational costs. An example is the combination of simulated moving bed (SMB) chromatography and selective crystallisation. However, the design of integrated processes is a difficult task. A shortcut method is presented that can serve as a tool for design and estimation of the potential of such processes. The approach requires only limited experimental data and thus allows for systematic parameter studies. The method is based on the determination of the purity-performance characteristic of the SMB process and rigorous application of mass balances. The use of relative mass fluxes allows derivation of simple algebraic expressions for essential process parameters. The significant potential of combining SMB and crystallisation is demonstrated for the example of the separation of mandelic acid enantiomers.     

Polymer blends based on the β-modification of polypropylene

iPP/sPP, iPP/rPP, iPP/PVDF and iPP/PA-6 blends, and their β-nucleated forms were prepared in the present study. The components of iPP/sPP and iPP/rPP blends are compatible in the molten state. The phase structure of the melt of iPP/PVDF and iPP/PA-6 blends is heterogeneous. The melting and crystallisation characteristics as well as the structure and polymorphic composition of these blends were studied by polarised light microscopy (PLM) and differential scanning calorimetry (DSC). When semicrystalline polymers are added to iPP, the most important factor of the formation a blend with β-crystalline phase is the α-nucleation effect of the second polymer. In the case of polymers with an α-nucleating effect, the temperature range of their crystallisation should be lower than that of β-iPP. β-nucleated iPP/PVDF and iPP/PA-6 blends are extreme examples showing that completely β-iPP matrix can not form even in the presence of a highly effective β-nucleant, because of the strong α-nucleating ability and higher crystallisation temperature range of PVDF and PA-6. We found that the β-crystallisation tendency of random propylene copolymers can be enhanced by adding an iPP homopolymer.     

Nonclassical nucleation towards separation and recycling science: Iron and aluminium (Oxy)(hydr)oxides

Separation, analysis and recycling technologies are of high interest for our modern societies, where colloidal iron and aluminium (hydr)oxides have important applications. However, there are significant gaps in the fundamental understanding of how these phases form in real systems. Classical nucleation theory cannot account for many experimental observations, and there is a dichotomy between the chemistry of hydrolysing/condensating systems and the physical notion of supersaturation. Reviewing parts of the established and recent literature, we demonstrate that concepts of nonclassical nucleation pathways can overcome these issues. This broader, chemistry-based conceptual framework has a high potential for advancing current applications, and developing new strategies towards separation, analysis and recycling applications, which seem to be urgently required for the future.     

成核剂含量对β晶相聚丙烯结晶与熔融行为的影响

用DSC研究了β成核剂含量对β聚丙烯在等温与非等温结晶条件下的结晶与熔融行为的影响,发现当成核剂含量为0.005％时,结晶焓△H_c、β晶的熔融焓△H_(mβ)及熔点T_(mβ)均为最大,而α晶的相对含量最小.广角X-衍射数据表明,成核剂含量高的试样的(301)衍射峰的相对强度下降,反映分子链排列的纵向有序性降低.根据聚丙烯分子在β成核剂上附生结晶的成核机理解释了上述结果.     

Nucleation kinetics of paracetamol–ethanol solutions from metastable zone widths

A study of the nucleation kinetics for a cooling crystallisation of paracetamol–ethanol solutions in a batch reactor is described in this paper. Metastable zone width (MSZW) experiments were conducted in order to estimate the nucleation kinetics of the system. Measured MSZWs can be affected by numerous process parameters, such as cooling rate, concentration, agitation rate, and working volume. Two theoretical approaches were employed to estimate the nucleation kinetics, the classical mass based approach of Nývlt, and a more recent approach by Kubota, which also considers number density. Both approaches were found to produce similar estimates for the nucleation rates of the paracetamol–ethanol solutions as a function of supersaturation for an assumed nucleus size of 10 μm. The theory of Kubota was found to predict satisfactory estimates for the induction time of the nucleation process from MSZW data. The induction time was observed to be independent of the solution temperature as suggested by Kubota’s theory. This is a novel finding and serves to validate the induction time theory of Kubota. In this investigation, MSZWs were observed to decrease with increased levels of agitation and found to be independent of working volume.     

Modelling of electrolyte mixtures with application to chemical equilibria in mixtures—prototypes of blood''s plasma and calcification of soft tissues

Modelling of the biologic solutions has a great importance for basic physicochemical backgrounds of the living processes, mechanism of the diseases and drugs action, etc. The modelling of the chemical equilibria in solution that served as a prototype of the blood plasma with application to calcification of the tissues is performed. The concentrations of molecular–ionic forms containing calcium and hydrogen cations and phosphate anions in the range of ionized-calcium and total phosphorus concentrations from 0.5 to 3.0 mM and at the solution pH of 7.1–7.8 were calculated. The activities of the ionized species were described in approach to Debye–Hückel's theory. The full set of the equilibria taking into consideration dissociation of the water, phosphoric acid, formation of both inert and ionic calcium phosphates was considered. The states of calcium hydrophosphate dihydrate CaHPO₄·2H₂O (CHPD), calcium phosphate Ca₃(PO₄)₂ (CP), calcium hydrophosphate-phosphate dihydrate Ca₄H(PO₄)₃·2H₂O (CHPPD) and hydroxyapatite Ca₃OH(PO₄)₃ (HA) with respect to the boundary of the region in which they crystallise were determined. A criterion has been introduced to characterize the degree of salt supersaturation with respect to crystallisation, which is based on the concentration distance between the states of a salt in solution and at the boundary of its crystallisation. This criterion is used to provide a quantitative characteristic of the supersaturation of the phosphates and their tendency to crystallise in blood's plasma. It was established that the most soluble of the phosphates, CaHPO₄·2H₂O, is undersaturated and the other phosphates are supersaturated with respect to crystallisation. Thus, this phosphate does not take part in the calcification, and this is the source for ionized calcium in a blood plasma from the soft tissues. The role of the other phosphates in calcification of the soft tissues is decreased in the series HA>CP>CHPPD. The dependencies of the supersaturation of the solution on the pH and on the concentrations of calcium and phosphorus in a mixture are discussed.     

Crystallisation of Ba1-xSrxZn2Si2O7 from BaO/SrO/ZnO/SiO2 glass with different ZrO2 and TiO2 concentrations

The effect of different nucleation agents such as ZrO₂ and TiO₂ was investigated for a first time with respect to their crystallisation behaviour in the glass system BaO-SrO-ZnO-SiO₂. In all studied glasses, a Ba_1-xSr_xZn₂Si₂O₇ (0.1 ≤ x ≤ 0.9) solid solution crystallized. This phase was first described in 2015 to possess a similar structure as the high temperature phase of BaZn₂Si₂O₇ and a thermal expansion close to zero or even negative. It may find applications e.g. as cook panels, telescope mirrors, and furnace windows. Kinetic parameters of the crystallisation process were determined by supplying different heating rates in a differential scanning calorimeter (DSC). The results were evaluated using the equations of Ozawa and Kissinger with respect to the activation energies. Furthermore, the Ozawa method was used for the determination of Avrami parameters, which provides further information on the nucleation and crystallisation processes. Scanning electron microscopy including electron backscatter diffraction (EBSD) was used to characterise the microstructure, to determine the crystallite size and the crystal orientation. For the characterisation of the occurring crystalline phases, X-ray diffraction was used.     

Thermal degradation and crystallisation studies of reactively compatibilised polymer blends

The thermal degradation and crystallisation behaviours of polyamide12/isotactic polypropylene (PA12/PP) blends were studied. Effects of blend ratio and compatibiliser concentration on the thermal degradation properties of the blends were analysed. The activation energy for degradation in compatibilised and uncompatibilised blends computed using Horowitz-Metzger equation was reported. The blend ratio as well as the presence of compatibiliser has significant effect on the thermal stability of the blends. Phase morphology was found to be one of the decisive factors that affected the thermal stability of both uncompatibilised and compatibilised blends. Melting and crystallisation behaviours of the blends in the presence and absence of compatibiliser were evaluated. It was observed that blending has no significant effect on the melting and crystallisation properties of PA12 and PP. Compatibilisation of 70/30 and 50/50 PA12/PP blends didn't affect the crystallisation and melting behaviours of PA12 and PP even though some discrepancies were observed.     

Crystallisation of a simulated borosilicate high-level waste glass produced on a full-scale vitrification line

A simulated (inactive) borosilicate high-level waste (HLW) glass was produced on a full-scale vitrification line with composition simulating vitrified oxide fuel (UO₂) reprocessing waste. As-cast samples were compositionally homogeneous (Type I microstructure) and/or compositionally inhomogeneous displaying compositional ‘banding’ and frequently containing ‘reprecipitated calcine’ (Type II microstructure). Crystal phases identified in as-cast samples were: tetragonal RuO₂, cubic Pd-Te alloy, cubic (Cr,Fe,Ni,Ru)₃O₄, trigonal Na₃Li(MoO₄)₂·6H₂O, ostensibly cubic Zr_{1 − x − y}Ce_xGd_yO_2 − 0.5y and a lanthanoid (Nd,Gd,La,Ce) silicate. Zr_{1 − x − y}Ce_xGd_yO_2 − 0.5y and lanthanoid (Nd,Gd,La,Ce) silicate were found exclusively in the Type II microstructure as component crystal phases of ‘reprecipitated calcine’. Heat treated samples (simulating the retarded cooling experienced by actual (active) borosilicate HLW glasses after pouring) displayed extensive crystallisation and cracking (Type A microstructure) and/or ‘banded’ crystallisation (Type B microstructure) depending on their parent (as-cast) microstructure (Type I and/or Type II respectively). Crystal phases identified in heat treated samples were: tetragonal SiO₂ (α-cristobalite), tetragonal (Na,Sr,Nd,La)MoO₄, cubic Ce_{1 − x − y}Zr_xGd_yO_2 − 0.5y, a Ni-rich phase, a lanthanoid (Nd,Gd,La,Ce) silicate and orthorhombic LiNaZrSi₆O₁₅ (zektzerite). α-cristobalite was found exclusively in the Type A microstructure, while lanthanoid (Nd,Gd,La,Ce) silicate and zektzerite were only found in the Type B microstructure. Potential host phases for HLW radionuclides are: Pd-Te alloy (¹⁰⁷Pd and ⁷⁹Se), (Cr,Fe,Ni,Ru)₃O₄ (⁶³Ni), Zr_{1 − x − y}Ce_xGd_yO_2 − 0.5y (⁹³Zr, Pu and U), both lanthanoid (Nd,Gd,La,Ce) silicates (Am and Cm), (Na,Sr,Nd,La)MoO₄ (⁹⁰Sr, Am and Cm), Ce_{1 − x − y}Zr_xGd_yO_2 − 0.5y (⁹³Zr, Pu and U), the Ni-rich phase (⁶³Ni) and zektzerite (⁹³Zr, ¹²⁶Sn and U). Cracking in samples was attributed to thermal expansion mismatch between the borosilicate HLW glass matrix and RuO₂, cristobalite (both α and β), (Na,Sr,Nd,La)MoO₄ and zektzerite on cooling. There was also a contribution from the cristobalite α-β phase transition.     

Crystallisation process on the stage of the gel-to-solid transformation in thermo-reversible polyethylene gels

The crystalline phase in gels and solid (gel derived) samples of ultra-high molecular weight polyethylene was studied using the low-frequency Raman spectroscopy and the differential scanning calorimetry methods. The Raman data evidence the presence in gels of tiny crystallites whose thickness (3-5 nm) depends on the sort of solvent used. After removal of the solvent by drying or squeezing the original gels, there appear some extra ordered regions (6-12 nm in size) coexisting in solid material with the primary crystallites which remain unchanged. It is concluded that the gel-to-solid transformation is accompanied by a secondary crystallisation process which is weakly (if ever) dependent on the incipient crystalline entities in gels.