Column Plate Number Research Articles

Experimental study and development of an improved sulfur–iodine cycle integrated with HI electrolysis for hydrogen production

The sulfur–iodine (SI or IS) thermochemical cycle assembled with solar or nuclear energy has been proposed as a large-scale, clean and renewable hydrogen production method. In present work, an improved SI cycle integrated with HI electrolysis for hydrogen production was developed according to experiments and simulation. The mathematical models of HI electrolysis using proton exchange membrane (PEM) electrolytic cell was developed, and then the user-defined module of HI electrolysis was set up through Aspen Plus and verified by experimental data. After designing and simulating the new flowsheet of the SI cycle based on HI electrolysis, 10 L/h of H2 and 5 L/h of O2 were obtained. The theoretic thermal efficiency of flowsheet reached 25–42% in terms of the utilization of waste heat. An ideal thermal efficiency of 33.3% through the proper internal heat exchange in the flowsheet was determined. Sensitivity analyses of parameters in the system were conducted. Increasing proton transfer number of PEM electrolytic cell in HI section improved the thermal efficiency of SI cycle. The ratio of distillate to feed rate and the plate number of distillation column in H2SO4 section were the most sensitive factors to the heat duty of overall SI cycle. The proposed new flowsheet for SI cycle is competitive to the flowsheets previously proposed in the field of flowsheet simplification.

Pressure swing distillation for the separation of methyl acetate‐methanol azeotrope

AbstractPressure swing distillation (PSD) process was used to separate methyl acetate‐methanol azeotrope. Through the phase diagram analysis, distillation sequence and technological process were determined. On the basis of the principle of the minimum total annual cost (TAC), design variables such as feeding position, reflux ratio, and column plate number were optimized and the optimal parameters were determined. The high‐pressure column (HPC) under various pressures were analysed. The economic results of the PSD without heat integration, with partial heat integration, and with full heat integration were compared. The comparison results indicate that the TAC of the PSD without heat integration is the highest. The PSD with partial integration and full heat integration can effectively reduce the total capital cost and total operating cost. Compared with the PSD without heat integration, the TACs of partial heat integration and full heat integration exhibit 27% and 30% savings, respectively. Therefore, the PSD with full heat integration is more economically reasonable for separating methyl acetate‐methanol azeotrope.

Influence of Radial Heterogeneity upon Columns of Different Lengths

A numerically calculated method was used to study the influence of radial heterogeneity upon columns of different lengths. In this study, we assumed the fourth-order polynomial distribution function of mobile phase flow velocity and the local efficiency. The results relating to column efficiencies and tailing factors show that long and high efficiency columns are influenced by radial heterogeneity more than the shorter and low efficiency columns are influenced. Radial heterogeneity has various effects on columns of different lengths. The results indicate that an extreme high efficiency column has a threshold of length. When the length exceeds the threshold, increasing length will not result in a significant increase in the column plate numbers. The influence of radial heterogeneity upon mobile phase flow velocity and local column efficiency also varies. The radial distribution of local efficiency can enhance the effects of the mobile phase flow velocity radial distribution.

Preparation and chromatographic performance of a eugenol-bonded silica gel stationary phase for high performance liquid chromatography

A eugenol-bonded silica gel stationary phase (EGSP) for high performance liquid chromatography ( HPLC) has been synthesized by the solid-liquid successive reaction method. The preparation process included two steps: firstly, γ-glycidoxypropyltrimethoxy-silane (KH-560) was covalently attached to the surface of spherical silica gel. Then the bonded silica gel continued to react with eugenol ligand, which was a plant active component, and obtained EGSP. The structure of EGSP was characterized by elemental analysis, thermogravimetric analysis and Fourier transform infrared spectroscopy. Using naphthalene as a probe, the column efficiency was tested under the mobile phase of acetonitrile-water (35:65, v/v) at a flow rate of 0.8 mL/min. The chromatographic properties and the retention mechanism of EGSP were evaluated by using neutral, basic and acidic analytes as solute probes. Meanwhile, the comparative study with C18 column and phenyl column was also carried out under the same chromatographic conditions. The result showed that the eugenol ligand was successfully bonded to the surface of silica gel with a 0.28 mmol/g of bonded amount, and the theoretical plate number of EGSP column was about 24 707 N/m. The EGSP appeared to be a kind of excellent reversed-phase stationary phase with suitable hydrophobicity and various synergistic sites. The eugenol ligand bonded on silica gel could first provide π-π interaction sites for different analytes because of its benzene ring and alkenyl. In addition, the methoxy groups of eugenol were responsible for dipole-dipole and hydrogen-bonding interactions between the ligand and solutes in the effective separation process. Comparing with traditional C18 column and phenyl column, EGSP has an advantage in the fast separation of polar compounds under simple experimental conditions.

Preparation and application of an emodin-bonded silica gel chromatographic column for high performance liquid chromatography

An emodin-bonded silica gel stationary phase (ESP) for high performance liquid chromatography has been synthesized by the intermediate method. The preparation process was as follows: γ-glycidoxypropyltrimethoxy silane (KH-560) firstly reacted with emodin ligand; then the intermediate was chemically immobilized to the surface of silica gel. Characterization of ESP was carried out with Fourier transform infrared spectroscopy (FTIR), elemental analysis and thermogravimetric analysis. Naphthalene was used as a probe to determine the column efficiency with methanol-water (60:40, v/v) as binary mobile phase at a flow rate of 0. 8 mL/min. In order to elucidate the related separation mechanism, ESP was used to separate a series of neutral, basic and acidic aromatic compounds, as well as a sample of wind medicated oil. The conventional C18 column and phenyl column were also tested under the same chromatographic conditions for comparison. The results showed that the emodin ligand was successfully bonded to the surface of spherical silica gel with a 0.23 mmol/g of bonded amount, and the theoretical plate number of ESP column was about 19,874 N/m. The coupling reagent chains and anthraquinone rings in ESP offered a structural basis for hydrophobic interaction. Meanwhile, the emodin ligands provided π-π or π-ρ charge transfer, hydrogen bonding, dipole-dipole action sites for different analytes. The synergistic reaction of various action sites endowed ESP column special and excellent chromatographic separation selectivity. And a baseline separation of polar compounds such as amines and phenols on ESP was easily achieved by using common and cheap methanol-water mobile phases without buffer salts. The experimental conditions were simple and convenient.

Studies on Citronellal Extract Column Reflux Ratio and Theoretical Plate Number Design

In this paper, the batch rectification operation is adopted to keep distillate constituting constant high vacuum, in the operation process, the operation of variable reflux ratio is carries out. Through studying the relational system of reflux ratio, column top product composition, rectification time and theoretical plate number, when the concentration of citronellal extract column product is 99%, the appropriate reflux ratio is 0.8-15, and the graphic method is used to design13 pieces of theoretical plate number of citronellal extract column, providing powerful data support for the process design of citronellal extract column.

Study on the Accurate Determination of Polycyclic Aromatic Hydrocarbons in Coal Tar Utilization

The determination of polycyclic aromatic hydrocarbons (PAHs) in coal tar was systematically studied by the high performance liquid chromatography (HPLC), in which involved separation, qualitative and quantitative determination of PAHs. The series of key techniques and experiences were summarized. To ensure finely separation of PAHs PAH, using C18 bonding silica gel column, mobile phase of methanol-water, and theoretical plate number of column more than 5600 were needed. For quantitative determination, the external standard (E-X) quantitative method and external standard - response factor (E-F) quantitative method were recommended. For accurately quantitative determine PAHs, the key technologies were recommended including choice of the optimum solvent of samples preparation and optimum concentration and using ultrasonic treatment, etc. In addition, some determination typical coal tars were also given and recommended. .

Study on the Accurate Determination of Polycyclic Aromatic Hydrocarbons in Coal Tar Utilization

The determination of polycyclic aromatic hydrocarbons (PAHs) in coal tar was systematically studied by the high performance liquid chromatography (HPLC), in which involved separation, qualitative and quantitative determination of PAHs. The series of key techniques and experiences were summarized. To ensure finely separation of PAHs PAH, using C18 bonding silica gel column, mobile phase of methanol-water, and theoretical plate number of column more than 5600 were needed. For quantitative determination, the external standard (E-X) quantitative method and external standard - response factor (E-F) quantitative method were recommended. For accurately quantitative determine PAHs, the key technologies were recommended including choice of the optimum solvent of samples preparation and optimum concentration and using ultrasonic treatment, etc. In addition, some determination typical coal tars were also given and recommended. .

The Impact of Reflux Ratio on Rectification Column Theoretical Plate Number

In this paper, the computer-aided calculation is introduced to study the influences of the reflux ratio on the theoretical plate number of rectification column. It is found that the number of theoretical plates of rectification column is increasing as the decreasing of the reflux ratio, which is mainly caused by the increasing of the plate number in rectifying section. On the other hand, it is found that when reflux ratio is reduced in small interval, the theoretical plate number is increased in a zigzag shape. This interesting phenomenon is analyzed in depth and a reasonable explanation is given.

New Progress of Plate Model of Chromatogram: Five Distinct Plate Numbers

The five plate numbers were peak plate number (q’), slip-mechanism plate number (q), theoretical plate number (n0), real plate number (n) and plate-model plate number (q0). Slip mechanism was introduced into plate model and then a new equation of elution curve was deduced. The relational expression of five plate numbers was deduced through the new equation. Peak plate number and slip-mechanism plate number were new plate numbers derived from slip mechanism, and the physical pictures of them was discussed. Peak plate number would be regarded as an asymmetry index of peak, as column plate number is regarded as an efficiency index of column.

Relationship of Five Plate Numbers in Chromatography

Slip mechanism and plate theory were utilized to the investigation of computing formulas of five plate numbers. Column plate number and peak plate number were two different concepts. Peak plate number was a new concept which came from slip mechanism. A good relation existed between the peak plate number and the asymmetry of practical peak of chromatogram. Peak plate number could be regarded as an asymmetry index of chromatogram peak, as column plate number is regarded as an efficiency index of column. The plate in slip mechanism was mobile, which was different from the fixed plate in plate theory. The five plate numbers were four kinds of column plate numbers and one kind of peak plate number (q’); the four column plate numbers were theoretical plate number (n0), real plate number (n), plate-model plate number (q0) and slip-mechanism plate number (q).

Sample enrichment by using monolithic precolumns in microcolumn liquid chromatography

An on-line sample enrichment system was designed using monolithic precolumns in microcolumn LC. The monolithic ODS capillary columns were prepared via in situ sol–gel processes. The enrichment efficiency of the monolithic columns was tested by using phthalates as the analytes. The relative standard deviations ( n=6) for the retention time, peak area and peak height were between 0.4 and 1.2%, 0.9 and 5.5% and 0.4 and 3.9%, respectively. The system was linear ( R 2>0.99) within the working sample concentration and sample volume ranges. Comparing to 0.2 μl injection with a typical sample injector, the theoretical plate number of a same separation column was increased by 3–6-fold when the precolumn unit was used for sample injection. The recoveries of the analytes were between 88 and 120%, and the sample volume that could be injected into the system was increased up to 5000-fold. The limits of detection were improved by more than 2000-fold and were between 0.21 and 0.87 ng ml −1 even with a UV absorbance detector. This system was applied to the determination of phthalates contained in laboratory distilled water and tap water samples.

Stationary-phase effects in gradient high-performance liquid chromatography

The type of the stationary phase for reversed-phase liquid chromatography significantly affects the sample polarity range that can be covered using gradients of organic solvents in water. The polarity range available for gradient separations of samples containing compounds differing in the lipophilic parts of the molecules can be characterized by “gradient lipophilic capacity”, Pl, based on the retention of standard compounds with a repeat lipophilic structural unit, such as a methylene group. The gradient lipophilic capacity is also suitable to characterize the separation possibilities of the columns in non-aqueous reversed-phase gradient elution of strongly non-polar compounds, such as triacylglycerols. In the same way, the suitability of various columns for reversed-phase gradient separations of oligomers can be characterized by “gradient oligomer capacity”, as demonstrated in the example of oligo(ethylene glycols). To enable a comparison of the properties of stationary phases independent of column efficiency and dimensions, the gradient lipophilic capacity or the gradient oligomer capacity should be normalized for a “standard” column plate number, gradient range and volume (in column hold-up volume units). The gradient lipophilic capacity or the gradient oligomer capacity and the number of compounds that can be resolved during a gradient run decrease as the initial concentration of the strong solvent in the mobile phase increases and (or) the gradient time decreases. These quantities can be used to select a suitable column and to adjust the optimum gradient profile (the initial composition of the mobile phase and the gradient steepness) with respect to the time of analysis and the number of oligomers or other compounds with regular repeat structural groups that can be resolved during the gradient run.

Modeling and optimization of enantioseparation by capillary electrochromatography.

Both electrophoretic and chromatographic transport mechanisms are combined in electrochromatographic separation. In this paper, we developed a model of enantioselectivity in capillary electrochromatography (CEC) which can be applied in the separation of both neutral and ionic compounds. The overall selectivity in enantioseparation is considered to be made up of two contributions: one is the intrinsic difference in formation constants of a pair of enantiomers, and the other is the conversion efficiency of the intrinsic difference into the apparent difference in the migration velocity. The model was illustrated through the chiral separation of (R)- and (S)-salsolinols. Under a positive electric field, enantioseparation of salsolinols was achieved on an ODS column with beta-cyclodextrin as a chiral mobile-phase additive. The experimental results are discussed in relation to the effect of separation parameters, such as the direction and size of electric field and properties of the stationary and mobile phases. It was demonstrated that if both electrophoretic and partitioning mechanisms produce positive effects, high overall selectivity in CEC can be obtained. For pressurized-driven electrochromatography, although the column efficiency is sacrificed due to the introduction of hydrodynamic flow, the increased selectivity significantly reduced the requirement of large column plate numbers for resolution.

Quantification of desferrioxamine, ferrioxamine and aluminoxamine by post-column derivatization high-performance liquid chromatography: Non-linear calibration resulting from second-order reaction kinetics

Desferrioxamine B is widely used as therapeutic agent for removal of excess body iron and, more recently, for removal of aluminium. A HPLC-based method for direct sensitive and reliable determination of ferrioxamine, desferrioxamine, aluminoxamine and related metabolites has been developed for use in pharmacokinetic studies. The method consists of complete separation of the analytes by an optimized mobile phase avoiding conversion of desferrioxamine to ferrioxamine by the analytical system and overcoming problems due to peak tailing properties of desferrioxamine. A post-column derivatization reaction with colourless fluoro-complexed iron converts all iron free species to ferrioxamine and allows quantification at 430 nm avoiding interference of UV-absorbing coelutes. This reaction might be of interest for other analytical procedures concerning iron chelators. The influence of the post-column reaction system on the column plate number is characterized. As the reaction rate of desferrioxamine and aluminoxamine with iron(III) is of second-order kinetics, a quadratic calibration function is observed, resulting from a compromise between residence time and peak broadening. A solid-phase extraction procedure is presented for extraction of the analytes from plasma. Limits of detection ( S/ N ratio of 3) were determined as 1.95 ng for ferrioxamine, 3.9 ng for aluminoxamine and 15.7 ng for desferrioxamine, expressed as on-column load. A new iron-free metabolite was identified with fast atom bombardment-mass spectrometry as N-hydroxylated desferrioxamine.

Maintaining fixed band spacing when changing column dimensions in gradient elution

In gradient elution separations, it may be required to change either column length (to increase resolution or shorten run time) or column diameter (for an increase in sensitivity or for preparative separations). In either of these changes of column dimensions, it is usually desired to maintain the same relative band spacing (selectivity), so as to increase resolution in proportion to (column plate number) 1/2 when increasing column length, or to maintain constant resolution when changing column diameter. A general rule for avoiding changes in band spacing in these situations is to maintain the quantity [(gradient time)×(flow-rate)/(column volume)] constant, while holding the initial and final gradient mobile phase compositions (%B) fixed. This rule is only valid as long as the equipment hold-up volume (dwell volume) is negligible, or if all sample components are strongly retained at the start of the gradient. When neither of the latter conditions apply, then significant changes in band spacing may result when changing column size. Rules are presented for recognizing this potential problem for a given sample/HPLC-equipment combination, and adjustments in separation conditions that can avoid this problem are discussed. Changes in band spacing as a result of change in column size are of special concern when developing procedures for preparative chromatography under gradient conditions.

Use of Alumina Support for the Separation of Ethoxylated Oligomer Surfactants According to the Length of the Ethyleneoxide Chain

Abstract The theoretical plate number, capacity factor, peak assymetry and separation factor of an alumina high-performance liquid chromatographic column were determined using nonylphenyl ethylene oxide oligomers as solutes and eluents containing n-hexane, dichloromethane, dioxane, tetrahydrofuran, chloroform and ethyl acetate. The relationship between the chromatographic characteristics and physicochemical parameters of the stronger component in the eluent was calculated by multivariate mathematical-statistical methods. It has been established that each solvent influences differently the chromatographic characteristics. The best separation was achieved by using n-hexane - dichloro-methane eluent. Calculation proved that the dielectric constant, dipole moment and the bulkiness of the solvent molecule have the highest impact on the separation capacity of the alumina column.

Changes in chiral selectivity with temperature for an ovomucoid protein-based column

The effect of temperature on the direct HPLC separation of drug enantiomers was studied for the commercially available ovomucoid protein chiral stationary phase. We confirm that temperature is a valuable experimental parameter for optimizing separations of racemic drugs. The resolution of certain acidic and basic drugs responds differently with temperature change. However, these resolution changes involve more than the effect of temperature on mobile phase viscosity that influences column plate numbers. A simple strategy involving the selection of pH, organic modifier and temperature is presented for optimizing separations of drug enantiomers with this column.

Computer simulation for the prediction of separation as a function of pH for reversed-phase high-performance liquid chromatography: II. Resolution as a function of simultaneous change in pH and solvent strength

The optimization of reversed-phase high-performance liquid chromatographic separation by the simultaneous variation of pH and solvent strength (%B) was studied for acidic (substituted benzoic acids) and basic samples (substituted anilines). The combination of these two variables was expected to be more useful than either variable alone. This proved to be the case for the benzoic acid sample, but not for the aniline sample. Column plate numbers were also studied for each sample and as a function of pH. With the exception of one compound (3,5-dimethylaniline) in one particular pH range (3.0–4.5), plate numbers of 12 000–20 000 were observed for each sample.

Impact of acidic/hydrothermal treatment on pore structural and chromatographic properties of porous silicas : I. The conventional approach

A series of commercial silicas and a laboratory made product were subjected to acidic/hydrothermal treatment with solutions of HCI, HNO 3, H 2SO 4 and HF. The concentration of acid and the temperature and duration of treatment were varied. The specific surface area, content of metal impurities, types and concentration of surface hydroxyl and siloxane groups and crystallinity were determined for native and treated silicas. Only changes in the structural order of the surface could be assessed by means of 19Si cross-polarization magic angle spinning NMR spectrometry and electron diffraction. The native and acid-treated silicas were surface modified to n-octyl derivatives and tested under reversed-phase conditions. A notable improvement in the column plate number and the asymmetry of the peaks was observed, whereas the solute capacity factors remained nearly unchanged. The effect of the conditions of acidic treatment (concentration, temperature and duration) was established by factorial experiments. Acidic/hydrothermal treatment caused a more ordered surface structure with quasi-crystalline domains, which improved the chromatographic mass-transfer kinetics and hence the column performance of acid-treated silicas.