渗透汽化技术在液体分离中的研究新进展

渗透汽化是近年膜科学研究中最活跃的领域之一,在分离液体混合物,尤其是痕量、微量物质的移除,近、共沸物质的分离等方面有独特优势。简要介绍了渗透汽化技术的历史及发展过程,着重介绍了近几年渗透汽化技术在液体分离方面的研究进展。从研究结果来看,从水溶液中分离有机物研究主要集中在醇、酯的分离。在有机物脱水方面,开发出了选择性更好、渗透量更高的膜,乙醇脱水也有不少新的研究成果。特别是在有机混合物分离方面,取得了长足的进展,可以分离更多的有机物。     

The separation of multicomponent mixtures by gas permeation

Two types of modules are most common in gas permeation: the hollow fibre module and the spiral wound module. With some simplifying assumptions regarding the flow pattern, the separation characteristics of such modules can be calculated for binary and ternary mixtures.More important in practice, however, is the separation of multicomponent mixtures. This paper discusses the design of multicomponent systems including cases where non-permeating components or carrier gases at the permeate side are present.The results of some calculations are discussed and compared with the usual short-cut method based on the assumption of a pseudo-binary mixture. The results demonstrate that the reduction of a multicomponent mixture to a pseudo-binary mixture is only reasonable when components of similar permeability are lumped together. Serious deviations with respect to membrane area or product composition must be expected for larger differences in permeabilities.     

新型有机分离体系渗透汽化膜材料

综述了固载活性基团促进传递膜、新型共聚物和树枝型聚合物材料在提高膜的选择性与渗透通量中的作用.介绍了从分子结构角度设计的材料在提高分离效果与成膜稳定性中的应用,指出了新型高聚物膜材料在渗透汽化分离有机混合物领域具有较好的工业化应用前景.     

Selection of the sequence of separation of ternary mixtures

Two optimization problems are considered. One of them is the problem of the sequence of separation of a ternary mixture in a two-step system for which the energy consumption in processes at given capacities is minimal, and the other is the problem of the optimal distribution of contact surfaces between the first and second steps. For thermal separation systems, the dependence of the maximum possible capacity of the system on the sequence of separation of components is analyzed.     

Some features of combustion of aluminothermic mixtures

Alma-Ata. Translated from Fizika Goreniya i Vzryva, Vol. 28, No. 1, pp. 46–51, January–February, 1992.     

连续精馏分离乙酸乙酯与丙酮体系的模拟研究

对制备超细高氯酸铵产生的废液即乙酸乙酯-丙酮混合液的分离过程进行了模拟研究.采用Aspen Plus化工模拟软件中的RadFrac模块进行连续精馏模拟,分别考察了塔板数、进料位置、回流比及塔顶出料量对分离效果的影响.结果表明:对于处理流量3 kg/h乙酸乙酯-丙酮的混合液,精馏塔在塔板数40,进料位置第16块塔板,回流...     

Simulated moving-bed for separation of mandelic acid racemic mixtures

Two enantiomers that constitute a racemate have different activities when employed as pharmaceuticals. Consequently, the pharmaceutical industry has been forced to market pure enantiomers instead of the racemic mixture. Simulated moving bed (SMB) is a chromatographic process that operates continuously without losing the enantiomeric purity of outlet streams from SMB. The present work describes the enantioseparation of mandelic acid in a labscale SMB unit. Chiral stationary phase was made by packing Kromasil TBB (O,O′-bis(4-tert-buylbenzoyl) -N,N′-diallyl-L-tartar diamid) gel into empty columns. The outlet streams were sampled and analyzed by an analytical HPLC. Analysis indicated that purity values range from 82% to 94% according to the change of extract stream flow rate.     

Computer simulation of phase separation in binary polymer mixtures

Phase separation of binary polymer mixtures was numerically simulated by solving the time-dependent Langevin equation with Flory–Huggins free energy in two dimensions by using a finite difference method. Spinodal decomposition following structure coarsening was calculated. Simulation results were verified by evaluating the evolution of the wave number obtained from the calculated phase structure by Fourier transformation. Then, computer experiments were carried out to investigate effects of volume fraction and polymer characters, the number of segments, and solubility parameter on morphology. The phase separation time, when the phase began to separate, decreased with deviating volume fraction from 0.5 and with decreasing number of segments and difference between solubility parameters. The difference between solubility parameters had the largest influence on the phase separation time among them and had two effects, the acceleration of phase separation and the restriction of structure coarsening. © 1995 John Wiley & Sons, Inc.     

A review of ternary azeotropic mixtures advanced separation strategies

In most multi-component systems, the predominant non-ideality occurs which lead to the occurrence of an azeotrope. The ternary systems classification and study are summarized in first part of this review. The next part covers thermodynamic knowledge of residue curve maps, univolatility and unidistribution curves. A feasibility criterion based on thermodynamic properties of ternary diagram is presented, they are considered as powerful tool for the flow-sheet development and conceptual design. Separation of azeotropic mixtures and close boiling mixtures require non-conventional distillation processes, among which the leading processes are pressure-swing distillation if the composition of the azeotrope changes significantly with pressure, azeotropic distillation, extractive distillation, reactive distillation, and salt-effect distillation. The final section provides an overview of concepts, history, and recent strategies in these non-conventional distillations.     

Theoretical basis of adsorption processes for separation of multicomponent mixtures

In this paper different frontal regimes are analysed during adsorptional separation of multicomponent mixtures. Account is taken of the main qualitative characteristics of interphase mass transfer in undefined porous media, consisting of porous grains of different internal structures and the boundary of phase change in physical adsorption.     

Feasible variants of separation in distillation of multicomponent azeotropic mixtures

A new efficient method for determining the feasible variants of separation is proposed. Unlike the method we published previously, the new method is necessary and sufficient for the trajectories for sections to join in both simple and complex columns. The method is based on the laws of arrangement of trees of reversible distillation trajectories and singular points for sections on branches of these trees.     

Modeling of nonstationary processes during separation of multicomponent isotope mixtures

The article presents a mathematical model for calculation of nonstationary hydraulic and separation processes in a gas centrifuge (GC) cascade for separation of multicomponent isotope mixtures. The model has been applied to calculate the parameters of nonstationary processes in a GC cascade for separation of krypton, germanium and tungsten isotopes. As a result, the specifics of the excess holdup distribution along the cascade stages has been identified, and variations of the isotope concentrations in a nonstationary process have been revealed. The data obtained show that the proposed mathematical model is able to adequately describe nonstationary hydraulic processes in GC cascades for separation of multicomponent isotope mixtures.

Highlights:

Mathematical model of cascade for separation of multicomponent isotope mixture has been developed.

The model verification has been done.

The isotope transient regularities into cascade during nonstationary processes has been identified.     

Efficient optimization-based design for the separation of heterogeneous azeotropic mixtures

Model-based design of separation processes for heterogeneous azeotropic mixtures is a challenging task. The multiplicity of the solutions of equilibrium calculations and the discontinuity due to the potential switching between homogeneous and heterogeneous mixtures on a tray severely complicate the application of deterministic optimization. This paper presents a novel computational approach to reliably determine phase stability and the correct equilibrium solutions in every iteration of the optimization. The approach builds on the decomposition of the optimization problem into a generic superstructure model and an implicit model for equilibrium and enthalpy calculations, which is integrated into the optimization problem by means of an external function. The phase states and equilibrium solutions are determined by means of a reliable homotopy continuation algorithm. An additional reformulation of equilibrium solutions and enthalpy calculations allows overcoming the discontinuity problems. Different case studies illustrate the applicability and show the potential of the proposed method.     

Vapour phase separation of alcohol-water mixtures by adsorption onto silicalite

The ability of unbound silicalite to selectively adsorb alcohols from vapour streams containing high concentrations of water has been studied using a small packed bed. The phenomenon of roll-up was observed for both water and each alcohol studied. The uptake of water was significant. The magnitude of each roll-up and the analysis of the breakthrough curves suggest that the rate of mass transfer in the crystalline structure of silicalite not only decreases as the carbon chain length increases for straight chain alcohols (from ethanol to pentanol) but also is higher for straight chain alcohols than for the corresponding branched chain isomers. Desorption studies also show that differences exist between the rates of mass transfer of water and alcohol. The breakthrough times and equilibrium capacities confirm that the adsorptive capacity of silicalite is strongly influenced by the shape, size and organophilic nature of the alcohol.     

Pervaporation separation of binary and ternary mixtures with polydimethylsiloxane membranes

This study dealt with the separation of binary water–phenol and water–methanol mixtures and ternary water–phenol–methanol mixtures by pervaporation (PV) with polydimethylsiloxane (PDMS) membranes. The effects of the operating conditions (feed temperature, feed concentration, and feed flow rate) on the separation performance for binary mixtures were investigated. An increase in temperature or concentration increased the total permeation flux and decreased the organic separation factor. In other words, an increase in the temperature or feed organic concentration increased the water flux more significantly than the organic compound flux, which resulted in a separation factor reduction. Also, an increase in the feed flow rate increased the total flux and separation factor because the boundary layer effects diminished. The vapor–liquid equilibrium separation factor (α_VLE) and pervaporation separation factor (α_PV) values for the PDMS membrane were calculated, and this showed that α_PV for the water–phenol mixture was greater than α_VLE. This means that the membrane was highly efficient for the PV separation of phenol from dilute aqueous solutions relative to the separation of methanol. This was due to the fact that phenol has a higher solubility parameter than methanol in silicone membranes. To study the effect of a third component on membrane performance, PV experiments were also carried out with water–phenol–methanol mixtures. The results for total permeation flux and the phenol separation factor for PDMS membranes in contact with water–phenol–methanol ternary mixtures are similar to those in contact with water–phenol binary mixtures. The phenol separation factor of the membrane in contact with the ternary mixture was slightly lower than that in contact with the binary mixture. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Enhanced separation of highly non-ideal mixtures with extractive heterogeneous-azeotropic distillation

The distillation based separation can be extremely complex if highly non-ideal mixtures are to be separated. In spite of different successfully applied unit operations there is still a possible way to improve the distillation technique and widen its toolbar. A new improvement in this area is the development of the extractive heterogeneous-azeotropic distillation (EHAD). This unit operation includes the merits of extractive- and heterogeneous-azeotropic distillations in one unit without extra material addition. Our work supports EHAD features with successful experiments compared with modelling and comparison with other separation structures proving that the application of EHAD makes the separation of extremely non-ideal mixtures possible on an easy, powerful, energy saving, and cost efficient way.