Temperature Gradient Method for Continuous Countercurrent Gas–Liquid Chromatography

Abstract

Continuous countercurrent gas–liquid chromatography (CCGLC), where the gas and liquid phases move countercurrently and the sample can be introduced continuously, is a method suitable for separating binary sample systems. The flow ratio of the gas and liquid phases (G/L) in CCGLC should be between the partition coefficients of the two components to be separated. However, the larger the difference between the G/L and the partition coefficient of one component, the higher the separation efficiency of the other component. By shifting the partition coefficients from the point of introduction of the sample to the directions of the gas and liquid flows, we believed a more efficient separation of the components would be achieved. A separation tower with a temperature gradient was constructed to create an inclined arrangement of the partition coefficient. With this system, the separation of stereoisomers was investigated, and 99.9% purity of trans-decahydronaphthalene was achieved.     

Polymer–water partition coefficients of extended range measured by using organic modifiers in the aqueous phase

A procedure for estimating equilibrium polymer–water partition coefficients over a broad range of solute hydrophobicity is presented and evaluated. The coefficients were calculated from the concentration change in the liquid phase and hydro-organic mixtures of varying proportions were used to extend the range. Three hydrophobic polymers (PP, PE, and EBA), two types of solvent (acetonitrile and alcohols) and 12 model solutes were used. The estimated polymer–water partition coefficients, log K_pw, ranged from −0.5 to 8.5. The coefficients correlated to other partitioning systems such as the calculated log P_{octanol–water} up to 14 and the retention factor (log k_w) in reversed-phase liquid chromatography.     

Theoretical study of sequential centrifugal partition chromatography

Sequential centrifugal partition chromatography (sCPC) is a novel cyclic liquid–liquid chromatographic process. Each cycle comprises two steps, which differ by the liquid phase used as a mobile phase (upper or lower phase) and its flow direction. The feed is continuously separated into two product streams, which are collected alternately. The process includes six (four flow rates and two‐step durations) interconnected operating parameters. In this work, by imposing a complete separation of a binary feed mixture and using the assumption of instantaneous solutes partition equilibrium, a set of constraints on the sCPC unit operating parameters is derived. Using these constraints, a region of complete separation, composed of a set of combinations of the two‐step times, can be defined for a preselected feed and mobile phase flow rates. The approach is validated by simulation of a binary mixture separation in a sCPC using the cell model. © 2012 American Institute of Chemical Engineers AIChE J, 59: 241–249, 2013     

Lipid molarity affects liquid/liquid aroma partitioning and its dynamic release from oil/water emulsions

Initial dynamic flavor release from oil/water emulsions containing different TAG phases was studied using a computerized apparatus and thermodesorption GC. A significant influence of lipid molarity on liquid/liquid partitioning and release of some flavor compounds was found. The release of the least hydrophobic compounds was not affected by any type of lipid. Hydrophobic compounds showed a positive correlation between their release and decreasing molarity of the lipid phase, that is, with increasing number of lipid molecules; only the most hydrophobic compounds did not show such a correlation. A strong linear correlation between low-melting TAG/water partition coefficients and lipid phase molarity was validated by volatile partition data of C6, C11, and C16 alkane/water systems. Lipid phase transition from the liquid to solid state did not affect flavor partitioning and release. Neither experimental nor theoretical octanol/water partition coefficients agreed with experimental TAG/water and alkane/water partition coefficients.     

A comparison of novel ozone-based systems and photocatalysis for the removal of water pollutants

Three ozone-based systems and a photocatalytic system have been compared for the removal of a reactive dyestuff, orange RO16, and 2-chlorophenol in relation to degradation performances and ozone and energy consumptions. These systems were (1) liquid/gas–ozone (LGO): ozone was applied as it is produced in the gas phase; (2) liquid/solid–ozone (LSO): ozone was adsorbed on particulate silica-based material and then applied to water; (3) liquid/liquid–ozone (LLO): ozone was dissolved in a water-immiscible solvent and then applied to water; and (4) photocatalytic system using titanium dioxide catalyst (PHC). All four systems were capable of degrading the pollutants but presented different characteristics. The LSO system offered the possibility of using long contact times for slow ozone reactions and the LLO system is most suitable for fast ozone reactions. Both systems offer the prospect of more efficient use of ozone by extracting specific pollutants away from the water phase to the solid or the solvent phases. The PHC system presented the lowest rates and the highest energy consumptions by a factor of up to 400 times as compared to the ozone-based systems. The four systems were classified on the basis of their energy consumption as follows: for the degradation of RO16 (LLO相似文献   

Modelling of mass transfer in combination with radical reactions

The diffusion-reaction equations for different model versions have been solved using a finite-differencing technique. In all models a reactant A is transferred from the gas to the liquid phase and reacts in the liquid with B to form P. The calculations comprised a simple stoichiometric model, a system with radical intermediates involved in the propagation steps and a version where also the termination reactions were included. The results show that the diffusion coefficients of radical intermediates can have significant influence on the profiles of concentrations and reaction rates near the G/L interface. Furthermore, it is shown that for very fast reactions differences in diffusion coefficients of the intermediates influence the by-product formation. For systems of two radical intermediates, the so-called mixed termination product is only formed in low quantities whereas the other two termination products dominate. The calculation of enhancement factors required in the design of a G/L reaction system can be performed with simplified models where the reactive intermediates do not occur in the expressions for the reaction rates. The optimum model for a specific design purpose can be found by tuning the functions that correlate the parameters of the complex model to the parameters of the simplified model. In principle it is possible to very easily evaluate a large number of alternatives.     

Contribution of adsorption and partition to the separation mechanism in gel chromatography on inorganic carriers

Gel permeation chromatography (GPC) calibration curves log hydrodynamic volume versus elution volumes were obtained from a series of single and mixed eluents for polystyrene on inorganic carriers. The observed calibration shifts were interpreted as a result of adsorption and partition effects on elution volume V_e. Secondary contributions to the separation mechanism can be qualitatively described by means of thermodynamic relations from liquid adsorption (LSC) and liquid partition (LLC) chromatography using the solubility parameters of the eluents. The universal calibration procedure based on the hydrodynamic volume of the coils is directly applicable only for systems in which adsorption and partition is approximately the same.     

A Computer Simulation of Linear Gel Permeation Chromatography

Abstract

A phenomenological model based on a set of partial differential equations and boundary conditions is proposed for chromatography and, in particular, for gel permeation chromatography. The intractable boundary value problem, which does not have a closed form solution, was handled through the use of numerical methods employing a very large and very fast computer (IBM 360/195). The chromatograms generated by the computer simulator were compared with experimental chromatograms of various molecular weight polymers. The computer generated overlay plots of the simulated and experimental chromatograms showed good agreement (the two plots almost superimposed). The effect of other parameters on the chromatogram, i.e., flow rate, stationary phase bead size, solute diffusion coefficient in the stationary and mobile phases, and the partition coefficient were also investigated.     

固相萃取．超高效液相串联质谱法同时测定食品中红色2G、酸性大红、酸性橙Ⅱ和酸性金黄G

建立了食品中红色2G、酸性大红、酸性橙Ⅱ和酸性金黄G非法色索的固相萃取超商效液相串联质谱测定方法。以氨水乙醇溶液作为提取溶剂,利用WAX弱阴离子交换固相萃取柱对样品进行净化。检出限红色2G0．050mg／L,酸性大红O．050mg／L,酸性橙110,010mg／L,酸性金黄GO．010mg／L;加标叫收为78％-105％。本方法灵敏、准确高效,可对4种水油溶色素进行测定及确证。     

反相液相色谱法测定废水中的马来酸和富马酸

建立了反相高效液相色谱同时分离分析废水中的马来酸和富马酸的方法。样品用流动相溶解稀释,以Krornasil-C18为色谱柱,流动相为甲醇和水(pH=2.53)(体积比为3∶97),检测波长为210 nm,外标法定量。结果表明,马来酸和富马酸分别在2.698～26.980 g/L、2.328～20.952g/L范围内线性关系良好(r0.9995)。该方法具有操作简便、快速、重现性好等特点,并应用于对马来酸废水处理工艺中进行分析。     

快速液相分析法测定化妆品中邻苯二甲酸酯类化合物

利用快速分析色谱柱(表面多孔层填料,Poroshell),对化妆品中10种邻苯二甲酸酯类化合物的检测方法加以改进,建立了快速液相分析检测方法.10种邻苯二甲酸酯类物质在1～800 mg/L范围内线性关系良好,检出限在0.5～1 mg/L之间,相对标准偏差在0.36％～2.35％之间.相对于常规分析方法,分析时间和有机溶剂用量均减少了2/3.该方法可在常规液相色谱仪上实现,具有较强的实用性和可操作性.     

Development of a more efficient emulsion liquid membrane system with a dilute polymer solution for extraction of penicillin G

So as to find a more efficient emulsion liquid membrane (ELM) system for extraction of penicillin G from simulated media, further study was done on batch and continuous ELM systems with a dilute polymer solution in addition to our previous ELM work examined in more detail in this work. The study was carried out in the batch ELM system varying membrane composition and Na₂CO₃ concentration in the internal phase. Compared to the previous work, the polymer-dissolved ELM system with higher concentrations of Na₂CO₃ in the internal phase and lower concentrations of surfactant in the membrane phase produced much higher extraction efficiency. Also, an optimized emulsion composition from the batch system was applied to continuous extraction of penicillin G in the extraction column of Oldshue–Rushton type, and in view of the fact that high enrichment ratio of penicillin G was still obtained, development of a practical ELM system for penicillin G extraction seemed feasible.     

Formation of a High-Temperature Liquid Phase During the Sintering of PbFe2/3W1/3O3

A high-temperature liquid phase (rather than a low-temperature liquid phase at 690°C as reported recently) has been demonstrated to form at 860°C on heating and to solidify at 840°C on cooling in PbFe_2/3O₃. This liquid phase not only promotes densification, but also induces the formation of rounded PbFe_2/3W_1/3O₃ grains during sintering at 870°C. Through slow cooling at a rate of 25°C/h after sintering, platelike grains, designated G phase, are found to form in a thin surface layer of specimens. This formation of platelike G phase is considered to be related to the solidification and recrystallization of the liquid phase exuded from the interior. The amount of the G phase on the surfaces decreases with the increase of cooling rates, indicating that fast cooling will lead the liquid phase to be solidified in the bulk of specimens. These results reveal that the microstructure of PbFe_2/3W_1/3O₃ is greatly affected by the high-temperature liquid phase; additionally, the slow cooling treatment seems to be a direct and effective method for removing the residual liquid phase from PbFe_2/3W_1/3O₃.     

Mass Transfer in Liquid–Liquid Systems

A formal criterion for determining the phase controlling mass transfer in liquid–liquid systems is proposed. Experimental data on mass transfer in the continuous phase are generalized for the external and mixed mass-transfer problems.     

Asymmetry of Peak Shapes in Linear Gas—Liquid Chromatography

Abstract

A mathematical model describing axial dispersion, interparticle mass transfer, intraparticle gas diffusion, and diffusion in a uniform thickness liquid film is used systematically to investigate the influence of intraparticle diffusivity, diffusivity in a stationary liquid phase (SLP), partition coefficient, and thickness of liquid film on the shape of the peaks in linear gas—liquid chromatography by converting Laplace transformed equations into time domain. The low diffusivities of intraparticle and/or SLP can cause the asymmetry and long tail in chromatographic peaks. A higher partition coefficient and the film thickness at low diffusivities also give skewed peaks. At a higher mass transfer rate, the peak becomes sharper. From these results a guide can be suggested to avoid the asymmetric condition of long-tailing peaks.     

5-甲基吡嗪-2-羧酸的HPLC分析研究

建立了利用阴离子交换柱高效液相色谱法分析5-甲基吡嗪-2-羧酸的方法。色谱柱为Hyper-sail SAX强阴离子交换柱,以0.020mol/L磷酸二氢钾缓冲液(pH值=2.50):乙腈=95:5为流动相,流速为:1.0 mL/min,紫外检测器波长为276nm,外标法定量。结果表明:5-甲基吡嗪-2-羧酸在0.016~0.16g/L范围内浓度与峰面积呈良好的线性关系(R2=0.9995),加标回收率为98.12%~102.19%。此法具有灵敏度高、准确可靠、操作简便、快速,可用于5-甲基吡嗪-2-羧酸产品的检测和中间控制分析。     

Characterization of absorbent polymers for the removal of volatile hydrophobic pollutants from air

BACKGROUND: An emerging innovation for the treatment of polluted air consists in using a liquid–solid biphasic system, in which the sequestering phase contains inert polymer beads. The different polymers tested here for this purpose were; Hytrel^® G3548L, Hytrel^® G4078W, styrene butadiene copolymer, 28% and 31%, silicone rubber, PEBAX^® 2533, and rubber tires. The selection of the most effective polymer(s) first requires a determination of the uptake of the pollutants by the solid phase in terms of key polymer properties such as partition coefficient, diffusion coefficient and biodegradability. RESULTS: A significant difference was found in the uptake levels of α‐pinene from the gas phase for the different polymers tested. Based on partition coefficient measurements, relatively non‐polar polymers such as Kraton^® tend to uptake α‐pinene better than polar ones, such as Hytrel^®. A reduction in the partition coefficient of α‐pinene into polymers in the presence of water has also been observed. It was also proven that the tested polymers are not biodegradable. CONCLUSIONS: The uptake of α‐pinene by the different polymers tested was determined and it was shown that such polymers could be used for air pollution control. Furthermore, their non‐biodegradability justifies their use as absorbents. This paper provides a new opportunity to work with biofilters (BFs)/biotrickling filters (BTFs) using polymers as a sequestering phase. Copyright © 2010 Society of Chemical Industry     

Explicit model predictive control of gas–liquid separation plant via orthogonal search tree partitioning

Solutions to constrained linear model predictive control (MPC) problems can be pre-computed off-line in an explicit form as a piecewise linear (PWL) state feedback defined on a polyhedral partition of the state space. This admits implementation at high sampling frequencies in real-time systems with high reliability and low software complexity. Recently, algorithms that determine an approximate explicit PWL state feedback solution by imposing an orthogonal search tree structure on the partition, have been developed, and it has been shown that they may offer computational advantages. This paper considers the application of an approximate approach to the design of an explicit model predictive controller for a two-input two-output laboratory gas–liquid separation plant, including experimental evaluation. The approximate explicit MPC controller achieves performance close to that of the conventional MPC, but requires only a fraction of the real-time computational machinery, thus leading to fast and reliable computations.     

高效液相色谱法测定化妆品中邻苯基苯酚的含量

建立了一种快速简便地测定化妆品中邻苯基苯酚的高效液相色谱法。实验以乙腈-水（v/v,65∶35）为流动相,流速1.0mL/min,检测波长245nm,进样体积5μL,检测化妆品中的邻苯基苯酚,结果显示邻苯基苯酚的保留时间为6min左右,线性范围5～100mg/L,化妆品样品中的最低检出限为0.01%,平均回收率为86.7%～99.9%,精密度（RSD）为0.9%～1.39%。该方法样品处理快速简便,分析方法准确可靠,适用于对各类化妆水、护肤膏和护肤霜中的邻苯基苯酚含量进行监控。     

Mathematische Modellierung von Wirbelschichtreaktoren

Mathematical modelling of fluidized bed reactors . Among the many fluidized bed models to be found in the literature, the two-phase model originally proposed by May has proved most suitable for accommodation of recent advances in flow mechanics: this model resolves the gas/solids fluidized bed into a bubble phase and a suspension phase surrounding the bubbles. Its limitation to slow reactions is a disadvantage. On the basis of the analogy between fluidized beds and gas/liquid systems, a general two-phase model that is valid for fast reactions has therefore been developed and its validity is confirmed by comparison with the experimental results obtained by other authors. The model describes mass transfer across the phase interface with the aid of the film theory known from gas/liquid reactor technology, and the reaction occurring in the suspension phase as a pseudo-homogeneous reaction. Since the dependence of the performance of fluidized bed reactors upon geometry is accounted for, the model can also be used for scale-up calculations. Its use is illustrated with the aid of design diagrams.