Height Equivalent To A Theoretical Plate Research Articles

Study of the mass transfer kinetics in a monolithic column

The purpose of this work is to investigate the mass transfer kinetics of butylbenzoate on a monolithic RPLC column, with methanol–water (65:35, v/v) as the mobile phase. We used the perturbation method, measuring the height equivalent to a theoretical plate (HETP) of the peaks obtained as the response to small pulses of solute injected on a concentration plateau. The equilibrium isotherm of butylbenzoate was previously determined by frontal analysis. It is well accounted for by a liquid–solid extended multilayer BET isotherm model. The equilibrium data derived from the pulse method are in excellent agreement with those of frontal analysis in the accessible concentration range of 0 to 8 g/dm 3. Plots of the HETP of small pulses, injected on eight different plateau concentrations, were acquired in a wide range of mobile phase flow velocities. The axial dispersion and the mass transfer kinetic coefficients were derived from these data. The validity of these measurements is discussed. The mass kinetics of butylbenzoate depends strongly on the plateau concentration. Processes involving adsorptive interactions between the solute and the stationary phase, e.g. surface diffusion and adsorption–desorption kinetics, combine in series to the external mass transfer kinetics and to effective pore diffusivity.

H-D-T cryogenic distillation experiments at TPL/JAERI in support of ITER

The hydrogen isotope separation system (ISS) using cryogenic distillation method is one of the key systems in a fuel cycle loop of a fusion reactor. The ISS for the International Thermonuclear Experimental Reactor (ITER), is characterized by its required flexibility for the variability of feed composition, which is not considered in the existing industrial distillation columns, so that the development of evaluation method of dynamic behavior, which is the base for the establishment of ISS control system, is essential as original technology. At the Tritium Process Laboratory in Japan Atomic Energy Research Institute (TPL/JAERI), H-D-T cryogenic distillation experiments have been carried out to acquire the systematic data for the design of the ISS for the ITER. The value of height equivalent to a theoretical plate (HETP) was estimated to be 5 cm by the results of present experiments and it was adopted in the ITER–ISS design. The in situ, multi-points and reliable high-speed gas analytical system with Laser Raman spectroscopy was successfully demonstrated in the experiment to analyze the hydrogen isotopes of H 2-HD-HT-D 2-DT-T 2 within 1 min with the analysis limit of 1000 ppm, which indicates that this system enables fine control of the ISS. The reliability of this system was also proved through its use without any mechanical trouble for more than 2 years. The analysis codes were developed and improved through the experiments, and it was succeeded to simulate the dynamic behavior of the distillation column. Through a series of the ISS experiments at the TPL/JAERI, effective design and effective operation of the ISS became to be possible.

Nitrogen Isotope Separation with Displacement Chromatography Using Cryptand Polymer

Chromatographic nitrogen isotope separation was experimentally studied in a break through manner. A solution of 0.4 mol.dm-3 NH4C1 in methanol was continuously fed at 0.12, 0.25 and 0.50 cm3.min-1 into a glass tube packed with cryptand(2B,2,1) polymer. The temperature of column was kept constant at 293 K by passing temperature-controlled water through a jacket. Nitrogen gas was generated from the effluent reacted with Ca(ClO)2 solution after removing methanol by vacuum distillation, and the ratio of 14N15N to 14N14N was measured with a mass spectrometer (Finnigan MAT252). NH4Cl concentrations in the samples were gravimetrically determined. An enrichment factor, which is defined as an equilibrium separation factor minus unity was determined to be 0.0025±0.0013. A HETP (height equivalent to a theoretical plate) was evaluated 0.5±0.2cm at 14cm-h-1. This is the first report on nitrogen isotope separation with cryptand polymer.

Nitrogen Isotope Separation with Displacement Chromatography Using Cryptand Polymer.

Chromatographic nitrogen isotope separation was experimentally studied in a break through manner. A solution of 0.4 mol.dm-3 NH4C1 in methanol was continuously fed at 0.12, 0.25 and 0.50 cm3.min-1 into a glass tube packed with cryptand(2B,2,1) polymer. The temperature of column was kept constant at 293 K by passing temperature-controlled water through a jacket. Nitrogen gas was generated from the effluent reacted with Ca(ClO)2 solution after removing methanol by vacuum distillation, and the ratio of 14N15N to 14N14N was measured with a mass spectrometer (Finnigan MAT252). NH4Cl concentrations in the samples were gravimetrically determined. An enrichment factor, which is defined as an equilibrium separation factor minus unity was determined to be 0.0025±0.0013. A HETP (height equivalent to a theoretical plate) was evaluated 0.5±0.2cm at 14cm-h-1. This is the first report on nitrogen isotope separation with cryptand polymer.

Hydraulic and Mass Transfer Characteristics of Packings for Absorption and Distillation Columns. Rauschert-Metall-Sattel-Rings

Hydraulic and mass transfer data including pressure drop, liquid holdup, gas- and liquid-side volumetric mass transfer coefficients and interfacial area are measured for Rauschert-Metall-Sattel-Rings (RMSR) 25, 40 and 50. The volumetric gas- and liquid-side mass transfer coefficients are measured using the absorption systems SO 2 /air-1 M NaOH and O 2 /air-water, respectively. The interfacial area is measured by the C02/air-l M NaOH absorption system. The data are described by 2- or 3-parameter empirical correlations and, with significantly larger scatter, also by well-known models taken from the literature. The results are compared with those for classical 25 and 50 mm metal Pall rings and with the results given by the Norton company for geometrically similar Intalox metal tower packing—packings for which a similar range of applications can be expected. Height equivalent to a theoretical plate (HETP) calculated from the mass transfer characteristics of the RMSR packings are compared with the experimentally measured HETP for the atmospheric distillation of isooctane-toluene, methanol-ethanol and ethanol-water.

Performance of an Endless-Belt Counter-Current Contactor for Vapor-Phase Adsorption: Dispersion and Residence Time Distribution

The residence time distribution and axial dispersion characteristics of an endless-belt counter-current adsorbent contactor have been studied experimentally and theoretically using, as a model system, the adsorption of CO2 from a N2 carrier on a silicalite adsorbent. Expressions for the Taylor dispersion coefficient, and hence the height equivalent to a theoretical plate (HETP), as a function of the gas flow rate and belt velocity have been derived (from the general Aris model) and are shown to provide an approximate indication of the system performance. However, dispersion in the experimental system is increased by mixing in the dead space within the apparatus, making it difficult to test the theory quantitatively. Although diffusion of CO2 in silicalite is rapid and the adsorbent layer is thin, the influence of mass transfer resistance is still appreciable. The experimental system (length of 50 cm) is shown to be equivalent to 5−10 theoretical stages (HETP 5−10 cm), depending on flow rate and belt velocity.

Characterization of Horizontal Distillation Column Equipped with Rotating Non-woven Fabric Packing.

The performance characteristics of a horizontal column equipped with 36 non-woven fabric elements that could be rotated in a direction normal to the column-sectional area were evaluated. Separation efficiency and pressure drop were measured under atmospheric pressure at total reflux, using the cyclohexane-heptane system. The stable operation range for a horizontal orientation was limited to the restricted region of the F-factor. However, separation efficiency, which was expressed in terms of HETP (height equivalent to a theoretical plate), at inclinations of 5 and 10 degrees was found to be approximately equal to that for a brush packing system with a horizontal orientation described in a previous work. Particularly, HETP values at a 5 degree inclination ranged from 0.078 to 0.16 m when the F-factor ranged from 0.07 to 0.27 m/s(kg/m3)1/2 at rotation speeds of 50 to 200 rpm. The pressure drop at inclinations of 5 and 10 degrees was larger than that for the brush packing system oriented horizontally by a factor of between 2.5 and 4.

Nuclear magnetic resonance studies of solvent flow through chromatographic columns: effect of packing density on flow patterns

NMR (nuclear magnetic resonance) techniques have been used to measure and characterise solvent flow through chromatographic columns. NMR imaging was used to track an injection of D 2O. PGSE (pulsed gradient spin echo) NMR was used to measure the flow-rate dependence of axial and transverse apparent diffusion. A combination of these two techniques (dynamic NMR imaging) gave the spatial distribution of the local velocity and apparent diffusion through a cross-section of the column. Significant column wall effects were observed and these effects were found to be highly dependent upon the column packing density. The column performance was assessed in terms of the HETP (height equivalent to a theoretical plate) determined by the NMR techniques employed.

Comparison of chromatographic methods for hydrogen isotope separation by Pd beds

Comparison among three chromatographic separation methods, i.e. hydrogen-displacement chromatography, self-displacement chromatography and frontal chromatography, is made in an experimental way using several gas mixtures of hydrogen and deuterium. There is small difference in the height equivalent to a theoretical plate (HETP) based on the plate theory among the three chromatographic techniques. The HETP value for the self-displacement chromatography is 3.9 cm, and that for the frontal or H 2-displacement chromatography is 3.0 cm at the same flow-rate. The self-displacement chromatography is more useful for the separation of a small amount of deuterium or tritium from other hydrogen isotopes under a moderate recovery ratio. Since the frontal chromatography uses no other gas than the sample, it is more convenient for the separation of deuterium from natural hydrogen even though a lower recovery ratio.

Neural Network Modeling of Structured Packing Height Equivalent to a Theoretical Plate

The height equivalent to a theoretical plate (HETP) of nine types of structured packing was successfully modeled using a neural network. The network was trained on data similar to that used to develop semiempirical mass-transfer models. The HETP was then predicted using the trained network. The neural network model yields a very accurate prediction of experimentally determined HETP values, and it is more accurate than a traditional semiempirical model. Using the neural network, it is also possible to rank the relative importance of input variables in determining the HETP. In particular, this work shows that the roughness of the structured packing surface is a very important input parameter.

Separative Analyses of Packed Water Distillation Column with Channeling Stage Model

In order to predict the HETP (Height Equivalent to a Theoretical Plate) values of packed water distillation columns, we developed the channeling stage model taking account of the effect of axial mixing in the liquid phase. The overall channeling coefficients were defined as in terms of the channeling coefficients ρ for the mass transfer through the phases and for the axial mixing in each phase. The coefficients ρ and ; were estimated for the packed column of 100 cm in length and 1.6 cm in inner diameter where Dixon gauze rings of 3 mm or 6 mm were packed. The HETP values calculated with the overall channeling coefficients ρ agreed well with the values obtained experimentally. By examining ρ and ;, we showed that the mass transfer efficiencies for 6 mm Dixon gauze ring per a unit length of the column were larger than those for 3 mm. On the other hand, the losses in degree of separation by the axial mixing for 6 mm were larger than those for 3 mm.

Use of equations for the description of experimental dependence of the height equivalent to a theoretical plate on carrier gas velocity in capillary gas–liquid chromatography

Optimal equation for fitting the experimental data on the height equivalent to a theoretical plate (HETP) versus carrier gas velocity in GLC was determined. The data obtained by authors and the literary data by other investigators were used for the comparative study of Van Deemter, Golay and the little known Golay–Guiochon equations. The Golay–Guiochon equation takes into account instrumental contribution and other sources of additional band broadening. Correlation coefficient R and Pirson’s criterion χ 2 were used as a criterion of the data correspondence to the equations. The Golay–Guiochon equation is the best for fitting of the experimental data in 71% considered examples, 19% experimental data may be fitted very precisely by the Van Deemter equation, the Golay equation is preferable for 7% experimental data only. Three percent experimental data may be fitted with the same precision by the Golay and the Van Deemter equations. The results obtained are of theoretical and practical interest. The Golay–Guiochon equation must be used more widely in analytical practice and physicochemical measurements.

Enhanced performance of expanded bed chromatography on rigid superporous adsorbent matrix

Rigid spherical macroporous adsorbent beads with surface hydroxyl groups were prepared by cross-linking of cellulose. These beads had diameter in the range 100–200 μm and a mean pore size of about 3 μm with about 60% pore volume. The matrix (bulk density ∼1600 kg m −3) could be expanded into a stable bed and used for protein chromatography. Chromatographic runs were performed on a 10 mm diameter column under non-retaining and retaining conditions on the prepared matrix (called Celbeads) and performance of the runs was measured in terms of the height equivalent to a theoretical plate (HETP). The HETP curves in both packed and expanded bed modes followed profiles typical of macroporous adsorbents, i.e. increasing and levelling with velocity. Unimpaired performance of the matrix at increasing flow-rates permitted expanded bed elution of adsorbed solutes without loss of efficiency in terms of purification factor and product concentration. As a model system, Celbeads was used to purify lactate dehydrogenase from porcine muscle homogenate by dye-affinity chromatography. The prepared matrix provided about 100 theoretical plates per meter for the enzyme system at a linear flow velocity of 1.27 cm min −1 in an expanded bed elution mode, and gave enzyme yields of 100% with a purification factor of 31 using an optimized procedure. The adsorbent could be cleaned in place with 5 M urea and used repeatedly without loss of performance.

Hydrogenating rates of twin columns packed with Pd and molecular sieve with an alternately counter-current flow for hydrogen isotope separation

Palladium and molecular sieve adsorbents are promising materials for hydrogen isotope separation judged from previous experimental data of the isotope separation factor, the absorption or adsorption rate constant and the height equivalent to a theoretical plate (HETP). In the present study, the hydrogen absorption or adsorption rates of twin beds packed, respectively, with alumina-supported Pd pellets and molecular sieve (MS-5A) pellets are experimentally determined as a basic study for developing a new type of hydrogen isotope separation system. Very narrow mass-transfer zones compared to the column length move through either of the two columns because of high absorption or adsorption rates. The hydrogen pressure in the zone decreases from the inlet pressure to zero until the front of the zone reaches the column end. The amount of hydrogen absorbed or adsorbed in the zone is almost independent of the hydrogen flow rate. The twin-bed system with an alternately counter-current flow for a semi-continuous isotope separation process is found to be operated effectively by heating–cooling cycles without any external pump.

Correlation of HETP and experimental variables in preparative liquid chromatography

HETP (Height Equivalent to a Theoretical Plate) is widely designated as the column efficiency in Chromatographic separations. The effects of experimental variables such as concentration, injection volume, flow rate and composition of the mobile phase, column diameter, and column length on HETP were investigated by preparative liquid chromatography. Water and methanol as an organic modifier were used as the mobile phase. A sample of thymidine was injected into C18 columns with different dimensions. From fifty experimental runs, it was shown that the larger amounts of sample and higher flow rates increased HETP and an optimum HETP existed at a column diameter of 7.8 mm for preparative packings used in this experiment. The experimental values of HETP were correlated into a quadratic equation with the interaction terms based on the logarithmic experimental values of the experimental variables ; its regression coefficient was 0.952. The experimental variables were simulated from the correlation equation, and their effects on HETP were discussed.

Height Equivalent to a Theoretical Plate Theory for Rectangular GC Columns

The theory for the height equivalent to a theoretical plate (HETP) of a miniature rectangular gas chromatographic (GC) column is developed in analogy to Golay's theory for an open tubular GC column. The HETP is similar to that for an open tubular column except for the nonequilibrium or mass-transfer term. Unlike prior theories, the nonequilibrium or mass-transfer term is complexly related to column geometry. The theory successfully predicts the performance of fast chromatography, in the form of both short microbore and micromachined columns. For a given column length, rectangular columns have lower HETPs than conventional capillary columns and higher volumetric flow rates. A good rule of thumb is that the resolution can be adjusted by selecting the column height (provided it is much less than the column width), and the volumetric flow of carrier gas can be adjusted by selecting the column width (or cross-sectional area). A satisfactory compromise is to use a low inlet pressure that also provides an HETP that remains nearly constant over a range of pressures.

Effect of development speed on separative performance of displacement chromatography using porous ion exchange resin for Li isotope separation

A series of displacement chromatography experiments using a porous ion exchange resin for Li isotope separation was performed using several development speeds. Chromatographic development at a high speed is preferable for practical use, but the degree of separation becomes smaller with increasing development speeds. The height equivalent to a theoretical plate (HETP) value, which is an important factor of separative performance, increased exponentially when the development speed was increased. As a new measure to take account of both HETP and development speed, a separation per unit time (SPUT) was defined. A maximum SPUT value was achieved when the development speed was of the order of 300 cm h −1 in the system using the porous ion exchange resin TITEC-H1.

Study of Dispersion in Packed Chromatographic Columns by Pulsed Field Gradient Nuclear Magnetic Resonance

Pulsed field gradient nuclear magnetic resonance (PFGNMR) allows the direct determination of the average value of the axial and transverse apparent dispersion coefficient in a packed bed over a certain volume of this bed. From these data, the dependence of the local value of the height equivalent to a theoretical plate (HETP) of a chromatographic column on the fluid velocity can be measured accurately. The results are shown to be exactly accounted for by the Giddings equation. The PFGNMR measurements are made over a very short period of time. Hence they give the value of the HETP averaged over a limited volume of packing and a short time. This value is markedly smaller than the one afforded by the classical methods of chromatography and which is derived from the width of the distribution of the residence time of a small sample. The difference is explained by systematic variations of the local mobile-phase velocity across the column. PFGNMR techniques also allow the determination of the tortuosity of the column packing in the absence of flow. Their results confirm that the apparent dispersion experienced by a molecule is a function of the duration of the observation, until the tortuosity of the packing is completely felt. The values obtained agree very well with those derived from classical chromatography determinations.

Flow-rate dependence of the height equivalent to a theoretical plate in nitrogen isotope separation by displacement chromatography

The effect of flow-rate in nitrogen isotope separation was studied for a wide range of fluid velocities using porous microreticular cation-exchange resin. The displacement chromatography was conducted from a band velocity of 6.3×10 −3 to 12.5 cm/min (or Reynolds number of 15–30 000). A sharp adsorbed ammonium band was maintained even at a band velocity of 12.5 cm/min; on the other hand, tilted and/or channeled boundaries of the band are enlarged in the low-flow-rate region. The effect of fluid velocity on the height equivalent to a theoretical plate (HETP) of isotope separation was evaluated in terms of Reynolds number. In the present work, the HETP is proportional to the square-root of the band velocity in the turbulent flow regime and inversely proportional to the fluid velocity in the laminar flow regime due to the longitudinal mixing which is caused by tilting and/or channeling at the band boundary.

Permeable packings and perfusion chromatography in protein separation

The use of permeable packings in perfusion chromatography for protein separation is reviewed. Mass transport mechanisms in large-pore materials include forced convection in addition to diffusive transport. The key concept in perfusion chromatography is the “augmented” diffusivity by convection which explains the improved efficiency of perfusive packings compared with conventional supports. An extended Van Deemter equation has t be appplied when calculating the height equivalent to a theoretical plate (HETP) of chromatographic columns with flow-through particles. It is shown that the effect of forced convective flow in pores is to drive the separation performance between diffusion-controlled and equilibrium limits. A methodology to understand mass transfer mechanisms in permeable packings is proposed. Experimental results for protein separation by high-performance liquid chromatography in new packing media are discussed. Simulated moving bed technology is addressed.