Column Sequences Research Articles

A simplified monobuffer multidimensional chromatography for high-throughput proteome fractionation

The complexity of the human serum proteome is attributed to both a large dynamic range of protein abundance, as much as 10 orders of magnitude, and a disproportionate few dozens of proteins representing as much as 99% of the total protein content. These characteristics make it beneficial to use a pre-fractionation step prior to any high-resolution analysis, such as mass spectrometry. The present method describes a unimodal multidimensional chromatography concept to rapidly achieve an effective fractionation of human serum that is directly amenable with surface-enhanced laser desorption/ionization (SELDI)-based mass spectrometry. This method is based on the use of a column composed of a superimposed sequence of sorbents. The assembly is first equilibrated with a single binding buffer and then loaded with the whole crude sample. As the sample crosses the different adsorbent layers proteins within are sequentially trapped according to the complementary properties vis-à-vis of the sorbent. Once the loading and capturing is achieved, the sequence of columns is disassembled and each column, containing different complement of proteins is eluted separately in a single step and under optimal elution conditions. When compared to classical single-chemistry fractionation based on, for example, anion-exchange and pH stepwise elution, the new proposed approach shows much lower protein overlap between fractions, and therefore, greater resolution. This results in a larger number of detectable species, and therefore, reinforces the power of discovery of new biomarkers. A significantly higher sensitivity for low-abundance species was additionally found as evidenced by spiking trials.

Rapid screening of design alternatives for nonideal multiproduct distillation processes

The determination of the minimum energy demand using shortcut methods based on the well-known Underwood method has become a widely used tool for rating the economic incentive towards the usage of complex heat integrated column configurations for the separation of multicomponent mixtures into three or more products. However, available methods are only valid for ideal mixtures. Fast and reliable methods for the assessment of the minimum energy demand of the separation of nonideal zeotropic and azeotropic multicomponent mixtures in thermally coupled columns are still missing. The method introduced here addresses the case of complex column configurations with and without heat integration. It is based on the decomposition of the process into sequences of simple columns. The minimum energy demand of each column is determined using the rectification body method (RBM). Application of the suggested design method allows rapid screening of the different process alternatives by ranking their overall energy demand, exergy consumption or utility cost. The influence of the appearance of multiple steady states for azeotropic mixtures on the design decision is also discussed. The method is illustrated with a nonideal zeotropic and two azeotropic multicomponent separation examples.

Dynamic programming and lower-bound approaches to the minimum binding problem

The Minimum Binding Problem is that given a 0-1 matrix, a sequence of columns is found such that in each row 1 's appear as consecutively as possible. A dynamic programming algorithm succeeds in solving the problem for limited instances. For larger instances, we consider obtaining lower-bounds. A strategy to improve the lower-bounds is also discussed. Computational experiments show the effectiveness of our lower-bounds.

Effect of settling time on aerobic granulation in sequencing batch reactor

The essential role of hydraulic settling time in the formation of aerobic granules was studied in four column sequencing batch reactors (R1–R4). Results showed that aerobic granules were successfully cultivated and became dominant only in the R4 operated at the shortest settling time of 5 min, while a mixture of aerobic granules and suspended sludge was observed in R1–R3 run at settling times of 20, 15 and 10 min, respectively. After the steady state was achieved, the respective settling times of R1–R3 was shortened from 20 to 5 min, from 15 to 2 min and from 10 to 1 min; as the result, aerobic granules completely displaced suspended sludge in these three reactors after two-week operation. It was found that cell surface hydrophobicity was improved significantly at short settling times. Analyses of the polyvalent metals contents in aerobic granules showed that the accumulation of calcium in aerobic granules was related to the settling time, however, the total content of iron, magnesium and aluminium in aerobic granules was much pretty lower than the granule calcium content and almost remained constant. It is obvious that a short settling time favours aerobic granulation, and one may expect to manipulate the formation and characteristics of aerobic granules by controlling settling time.

The effect of upflow air velocity on the structure of aerobic granules cultivated in a sequencing batch reactor

The effect of upflow air velocity on the formation and structure of aerobic granules was studied in three column sequencing batch reactors. Upflow aeration would be the major cause of hydrodynamic shear force in the column reactor. Results showed that high upflow air velocity resulted in more compact, denser, rounder, stronger and smaller aerobic granules, while high biomass retention in the reactor was achieved. It was found that high upflow air velocity could induce granular sludge to secrete more cell polysaccharides which in turn contributed to the compact and strong structure. It appears from this study that the structure of aerobic granules could be controlled by manipulating the upflow air velocity.

Temperature Collocation Algorithm for Fast and Robust Distillation Design

In this paper, we describe a new minimum bubble-point distance (MIDI) algorithm for assessing the feasibility of a desired distillation specification. The algorithm computes the rectifying and stripping temperature profiles by temperature collocation on finite elements with orthogonal polynomials. We discovered the beneficial use of a dimensionless equilibrium tray temperature as an independent variable. This novel choice is bounded between 0 and 1, improves the numerical quality of the design problem formulation, and is well-behaved even in the vicinity of pinch regions. It also employs the fixed points of column sections as collocation points. Adaptive-element boundary placement at saddle temperatures can effectively overcome problems with numerical instability near pinch regions. Extensions of our MIDI algorithm to the calculation of the minimum and maximum refluxes are also introduced. We show the application of this algorithm in the separation of quaternary mixtures and provide an outlook of the methodology for optimal column sequencing. Cases studies demonstrate the algorithm's robustness and reliability.

Design and control for recycle plants with heat-integrated separators

This work analyzes the tradeoff between steady-state economics and dynamic controllability for heat-integrated recycle plants. The process consists of one reactor, two distillation columns, and two recycle streams first studied by Tyreus and Luyben (Ind. Eng. Chem. Res. 32 (1993) 1154) and further explored by Cheng and Yu (A.I.Ch.E. J. 49 (2003) 682) and, in this work, the two distillation columns are heat integrated. The design problem differs from typical column sequencing and heat-integration design, because we can design the reactor composition. Optimal trajectories for heat-integrated recycle plants with direct and indirect sequences are analyzed as the reactor composition of C ( z C ) varies. Provided with correct direction for heat integration, at any given z C , the flowsheet is established for both sequences. It turns out the heat-integrated recycle plant with direct sequence is economically optimal throughout the entire range of z C . For dynamic controllability, the reachable production range is identified as the recycle ratios (recycle flow rate/production rate) vary. Results show that the steady-state controllability deteriorates gradually as the degree of heat integration increases and, to the extreme, at the 50% energy saving line, we have lost one control degree of freedom. However, if the recycle plant is optimally designed ( z C ≈0.6), acceptable turndown ratio is observed and little tradeoff between steady-state economics and dynamic operability may result. Finally, rigorous nonlinear simulations are used to test control performance of different process configurations (with and without heat integration). The results reveal that improved control can be achieved for well-designed heat-integrated recycle plants (compared to the plants without energy integration). More importantly, better performance is achieved with up to 40% energy saving and close to 20% saving in total annual cost.

Shortcut Models for Retrofit Design of Distillation Columns

Shortcut models are well established for grassroots design of distillation columns and have been widely applied. However, no shortcut models are available that address retrofit. Shortcut models are quicker to solve, do not have significant convergence problems and are more robust than rigorous models for column optimization. In particular, shortcut models for retrofit would be valuable for evaluating retrofit design options, for improving the performance of existing distillation systems (columns and heat recovery systems) and can be combined with detailed heat-integration models for optimizing existing heat-integrated distillation systems. This paper presents retrofit shortcut models for design of both reboiled and steam-stripped distillation columns. These models are primarily based on a modified Underwood method, the Gilliland and Kirkbride correlations, the Fenske equation and the material balances. The retrofit models are applicable for simple distillation columns, sequences of simple distillation columns, and complex distillation configurations, including columns with side-strippers and side-rectifiers. The models fix both the column configurations and the operating conditions, including steam flow rates, and calculate the product flow rates, temperatures and compositions, and the various heat duties. A comparison of the model results with those of rigorous models of existing distillation columns is presented to validate the model.

Synthesis of distillation sequences for separating multicomponent azeotropic mixtures

An automatic procedure for the synthesis of sequences of distillation columns for separating homogeneous multicomponent azeotropic mixtures is developed. Key to the approach is the use of sets of compositions, or ‘product regions’, to specify product compositions. The synthesis procedure is implemented in two stages. The first stage consists of identifying classes of splits. Each class of split may be characterised as either feasible or potentially feasible. The synthesis procedure systematically combines these classes of splits to generate column sequences that satisfy a pre-determined separation requirement. The second stage of the synthesis procedure assesses the feasibility of a proposed flowsheet once the recycle options have been defined. Preliminary design of each column in the sequence can be performed. The feasibility assessment procedure will form the basis for systematic flowsheet generation and optimisation.

Operation of Homogeneous Azeotropic Distillation Column Sequences

A self-optimizing control concept is provided for sequences of three homogeneous azeotropic distillation columns with two recycles separating a ternary feed of a 020 mixture that has two simple distillation regions that are separated by a residue curve boundary. Studying a case with reduced complexity (columns of infinite length operated at infinite reflux), one of the two recycles (the entrainer recycle) is identified as the key manipulated variable for ensuring optimal operation of the sequence. Different setups of the scheme have different optimal feed regions. The theoretical results are illustrated with rigorous simulations of a 020 mixture: methanol (which acts as an entrainer), 2-propanol, and water. Dynamic simulations confirm that the process operates robustly by using the (L/D)QR scheme for the individual columns and one additional control loop that controls the methanol (entrainer) composition of the distillate by manipulation of the overall feed of one column. Dynamic simulations also confirm that column profiles can cross residue curve boundaries, distillation boundaries, and even azeotropes if the feed composition is changed such that a column profile is only feasible in the other distillation region.

Inhibition of free ammonia to the formation of aerobic granules

This study investigated the inhibition of free ammonia to the development of aerobic granules for simultaneous organic carbon removal and nitrification in sequencing batch reactors. Five column sequencing batch reactors (SBRs) were operated at different N/COD ratios in the range of 5/100 to 30/100. Results showed that aerobic granules formed only when the free ammonia concentration were less than 23.5 mg l −1, and nitrification was completely inhibited at a free ammonia concentration greater than 10 mg l −1. It was found that the specific oxygen utilization rates of heterotrophic and nitrifying bacteria were reduced by a factor 5 and 2.5 as the free ammonia concentration increased from 2.5 to 39.6 mg N l −1. Free ammonia resulted in a significant decrease of cell hydrophobicity, and also repressed the production of cell polysaccharides. These would be responsible for the failure of aerobic granulation at high free ammonia concentrations. This study probably for the first time demonstrated that free ammonia could hinder the formation of aerobic granules through its inhibition to energy metabolism of microorganisms.

Controllability of Different Multicomponent Distillation Arrangements

In this work, the controllability of different distillation arrangements for the separation of ternary mixtures is compared. At the same time, the energetic efficiency of each one of the arrangements is analyzed. Specifically, the direct and indirect sequences of columns, the columns with side sections, and the divided wall column (DWC) are considered. To compare the controllability of the different arrangements, the preferred control structures are searched. For the DWC, operating conditions that favor controllability are discussed. Also, the arrangements have been compared under different design conditions.

Serially coupled capillary columns supercritical fluid chromatography with a coupling restrictor.

A serially coupled column system for capillary supercritical fluid chromatography was constructed by connecting two capillary columns of different polarities using or without using a coupling restrictor. The influence of the column sequence, the size of the coupling restrictor and the column temperature on the polarity of the system were studied. The system without a coupling restrictor (the directly coupled system) provided an intermediate polarity between two columns, depending on the column geometry, such as the film thickness and column length, although it slightly shifted to that of the first column. In the system with a coupling restrictor, the contribution of the second column to the overall retention increased with its resistance. The use of a coupling restrictor allowed to control the polarity of the coupled system virtually over the whole range between two columns. The temperature was an additional effective parameter for tuning the polarity of the system.

An experimental simulation of distillation column concentration profiles using a batch apparatus

There has been a growing interest in the use of residue curves for the preliminary design and sequencing of distillation columns. Residue curves are used not only to predict composition changes in separation processes, but also to determine the feasibility of proposed separations, and flowsheet development (Chem. Eng. Sci. 33 (1977) 281). An experimental technique has been developed for the measurement of these residue curves. (Distillation & absorption ’97, Inst. Chem. Eng. 1 (1997) 187). It can be shown that the time-dependent composition profiles obtained in a modified form of this apparatus are mathematically equivalent to the position-dependent profiles in a continuous distillation column. Hence, it is possible to experimentally simulate a distillation column profile in a small batch apparatus using only small quantities of material. The modified apparatus consists of a still immersed in a heated oil bath so that a liquid feed is continuously supplied to the still. Samples of liquid are then analysed over time using a gas chromatograph. The results from an experimental system have been compared to available information and simulations to determine the accuracy of the apparatus. This technique has several advantages over working with distillation columns, firstly in the sample size required, and secondly in the ease of operation. The method allows quick and low-cost measurements of the concentration variables that model a distillation column. The information obtained this way could prove useful for the selection of feasible systems and for finding minimum reflux requirements. It could also be very valuable for screening of complex systems where only small amounts of material are available and simulations may be very difficult.

Application of Isooctane to the Dehydration of Ethanol. Design of a Column Sequence To Obtain Absolute Ethanol by Heterogeneous Azeotropic Distillation

Consistent vapor−liquid (VLE) and vapor−liquid−liquid equilibrium (VLLE) data for the ternary system water + ethanol + isooctane (2,2,4-trimethylpentane) are reported at 101.3 kPa at temperatures in the range of 341−352 K. An all-glass, dynamic recirculating still equipped with an ultrasonic homogenizer has been used in the determination of the VLLE. The experimental data obtained demonstrates the existence of a ternary heterogeneous azeotrope at 68.7 °C with a composition of 0.198, 0.436, and 0.366 mole fractions of water, ethanol, and isooctane, respectively. The VLLE data were correlated simultaneously with VLE data by using the UNIQUAC model. The parameters obtained allow the development of suitable distillation sequences to obtain pure ethanol or a mixture of ethanol and isooctane.

Conceptual design aspects of reactive distillation processes for ideal binary mixtures

A comparative study on the conceptual design of reactive distillation process configurations is presented, considering the reversible reaction A 1⇔A 2 in an ideal binary mixture as simple model system. The analysed flow schemes are a reactor-distillation column sequence with an external recycle loop, the same recycle system with a prereactor, a nonreactive distillation column on top of a reactive reboiler, a fully reactive distillation column, and a hybrid distillation column combining a reactive and a nonreactive section. For these configurations, the design aspects are discussed in terms of the most important operating parameters, kinetic parameters and design parameters.

Synthesis and design of heterogeneous separation systems with recycle streams

Geometric methods are one of the most valuable tools for distillation process synthesis and design. The graphical representation of azeotropes, residue curves, distillation regions, and distillation boundaries provide designers with intuition, a wealth of knowledge about the entire composition space and quantitative results. In this paper we show how residue curve maps and geometric methods can be used in the synthesis and design of sequences of complex heterogeneous azeotropic distillation columns. A new algorithm for the design of heterogeneous azeotropic distillation column with top decanter is presented and applied in two design case studies of column sequences with recycle streams and top decanters. In both the cases, a feasible structure has been quickly found based on information obtained by examining the entire composition space.

Influence of phenol on cultures of acetate-fed aerobic granular sludge.

This paper attempts to investigate the inhibition of phenol on the acetate utilization in acetate-fed aerobic granular sludge culture. Acetate-fed aerobic granules with a mean diameter of 1.0 mm were predeveloped in a column sequencing aerobic sludge blanket reactor. The present study looked into the utilization kinetics of acetate by acetate-fed aerobic granules in the presence of different phenol concentrations ranging from 0 mg l(-1) to 50 mg l(-1). For this purpose, batch experiments were conducted at 25 degrees C, while the initial biomass and acetate concentrations were in a range of 109-186 mg mixed liquor suspended solids (MLSS) l(-1) and 185-300 mg acetate-chemical oxygen demand (COD) l(-1). Results showed that the utilization of acetate in the presence of phenol was subject to a zero-order reaction kinetics. The relative phenol concentration in terms of the ratio of initial phenol concentration (C(p)) to initial biomass concentration (X(0)) was used to describe the real inhibitory strength of phenol imposed on acetate-fed aerobic granules. When the C(p)/X(0) ratio increased from 0 to 0.19 mg phenol mg(-1) MLSS, the zero-order reaction rate constant of acetate dropped from 1.15 mg l(-1) min(-1) to 0.38 mg l(-1) min(-1), and a similar trend was also observed in specific oxygen utilization rate. As compared to the control test without addition of phenol, the acetate-COD removal efficiency was reduced by nearly 50% at a C(p)/X(0) value of 0.19 mg phenol mg(-1) MLSS. It was found that biodegradation of phenol was negligible in acetate-fed aerobic granular sludge batch culture. It appears that phenol can seriously repress the utilization of acetate in the acetate-fed aerobic granular sludge batch cultures. A simple zero-order reaction model could adequately describe the utilization of acetate by acetate-fed aerobic granules in the presence of phenol. It is expected that this study would lead to a better understanding of the behaviour of acetate-fed aerobic granules in the presence of inhibitory organic compounds.

A simple method for systematic synthesis of thermally integrated distillation sequences

Thermodynamic approach to heat integration of processes involving separation of multicomponent mixtures is described. An integrability criterion based on geometrical presentation of distillation columns in temperature–enthalpy flow rate diagram was tested by rigorous simulation of distillation columns. The integrability criterion for distillation columns sequence was defined as the minimum sum of products of intracolumn temperatures and their heat flow rates (Min-criterion). Distillation columns sequences were studied according to their profitability in heat integration. Energy-pinch analysis was used for the synthesis of the best heat integrated distillation system. The representation using extended grand composite curve was demonstrated to be a very convenient one for understanding and evaluating the heat integration. The selection of possible distillation columns sequences using rising values of the integrability criterion gave a very good approximation towards the best sequence of heat integrated distillation columns when compared to their total annual cost. Their estimation using rigorous models of distillation columns was shown to be better than using short cut models. The method allows alternative distillation sequences to be evaluated using rigorous calculations, prior to column design. The method is demonstrated with three five- and six-components example problems.

Multicomponent homogeneous azeotropic distillation 3. Column sequence synthesis

An algorithmic distillation column sequence synthesis procedure for multicomponent azeotropic mixtures is proposed. The synthesis procedure is divided into several stages, and makes use of the feasibility test for classes of splits, as defined by Thong and Jobson (Chem. Eng. Sci. (2001a) submitted), to systematically generate a range of feasible and potentially feasible column sequences for a specified separation requirement. A set of rules is applied to generate a recycle superstructure for every identified sequence. Stream compositions and recycles are then finalised. Column design methods presented in Thong and Jobson (Chem. Eng. Sci. (2001b) submitted) are then applied to every column in the sequence.