A versatile model for simulation of reaction and nonequilibrium dynamics in multicomponent fixed-bed adsorption processes

Greywater characteristics, impacts, treatment, and reclamation using adsorption processes towards the circular economy

The gap between water demand and available water supply led to wastewater treatment, particularly greywater. Due to specific characteristics of grey wastewater, treatment and recycling of this type of wastewater capture global attention. This paper presents a literature review of the remediation of greywater by adsorption processes. Besides, the reclamation of the grey wastewater in the context of the circular economy is highlighted. In this regard, the characterization of various types of grey wastewater, the potential risks associated with greywater, and the properties of reclaimed water as per the regulation or guideline are summarized. These standards vary based on the application of reused water and from a country to another country. Furthermore, this review elucidates the adsorption process in terms of the type of adsorbents, modification of adsorbents and their regeneration process, adsorption isotherm, kinetics and thermodynamic of adsorption, and optimization of adsorption system. Finally, the removal of different pollutants from greywater by various adsorbents and techno-economic aspects are illustrated.

Constant-pattern design method for displacement chromatography

Displacement chromatography can be used for the purification of many types of chemicals and biochemicals. In the constant-pattern mode, this method can be used for concentrating and separating various mixtures, leading to higher yields and sorbent productivities than elution chromatography. There are, however, no commercial-scale applications of displacement chromatography. One major barrier is the difficulty in specifying the design variables for reaching a constant-pattern state. A second barrier is that productivity is limited when the feed mixture contains a minority component. In this study, a constant-pattern design method is developed to overcome the first barrier. Theoretical analyses and strategically chosen combinations of key dimensionless groups are used for reducing the multi-dimensional parameter space into a two-dimensional space. Systematic rate model simulations are used to find a general correlation, which divides the two-dimensional space into a transient region and a constant-pattern region. A predictive design method based on the general correlation is developed to find the designs for achieving required product purities and yields with the highest productivities. The design method was shown to increase significantly the productivities or yields for the separations of three binary mixtures. To overcome the second barrier, a multi-zone displacement chromatography method is presented for dividing the separation tasks in multiple zones. For a specific ternary mixture containing a minority component, the sorbent productivity for a two-zone design was 680 times higher than that of a single-column design. This method can be used for developing efficient displacement chromatography processes for purifying a wide range of complex mixtures.

Speedy standing wave design and simulated moving bed splitting strategies for the separation of ternary mixtures with linear isotherms

Simulated Moving Bed (SMB) has advantages over batch chromatography in terms of productivity and solvent efficiency. However, SMB applications in large scale production are still limited because of the many design parameters that must be specified and the multiple splitting strategies that can be implemented. To overcome these barriers, this study extends the Speedy Standing Wave Design (SSWD) method of Weeden and Wang for binary linear systems to ternary linear adsorption systems. The dimensionless operating parameters, sorbent productivity, and solvent efficiency can be quickly calculated without process simulations. SSWD also gives an overview of the productivity and solvent efficiency as a function of two key dimensionless groups. This overview can be used for optimization of separation costs and for comparison of splitting strategies. The SSWD method was verified using rate model simulations for the separation of three amino acids. The simulated yields agree with the SSWD target yields within 1% for all components. The example was also used to illustrate the key design rules for ternary separations. High productivity and solvent efficiency can be achieved with a large difference in the retention factors of the heavy key and light key, which are the components that define the split of the feed between extract and raffinate products. For ternary ideal systems, solvent efficiency is inversely proportional to the largest difference in retention factors. For this reason, minimizing the overall range of retention factors can significantly improve the solvent efficiency and product concentration without sacrificing productivity. If more than one SMB is needed, the easiest split should be done first for higher productivity, solvent efficiency, and product concentration. In the example case study, both the productivity and solvent efficiency were about an order of magnitude higher when the easiest split was done in the first ring. The SSWD method can be used to design a wide array of multi-component separations with high yield, productivity, and solvent efficiency.

A Solution-Based Approach for Mo-99 Production: Considerations for Nitrate versus Sulfate Media

Molybdenum-99 is the parent of Technetium-99m, which is used in nearly 80% of all nuclear medicine procedures. The medical community has been plagued by Mo-99 shortages due to aging reactors, such as the NRU (National Research Universal) reactor in Canada. There are currently no US producers of Mo-99, and NRU is scheduled for shutdown in 2016, which means that another Mo-99 shortage is imminent unless a potential domestic Mo-99 producer fills the void. Argonne National Laboratory is assisting two potential domestic suppliers of Mo-99 by examining the effects of a uranyl nitrate versus a uranyl sulfate target solution configuration on Mo-99 production. Uranyl nitrate solutions are easier to prepare and do not generate detectable amounts of peroxide upon irradiation, but a high radiation field can lead to a large increase in pH, which can lead to the precipitation of fission products and uranyl hydroxides. Uranyl sulfate solutions are more difficult to prepare, and enough peroxide is generated during irradiation to cause precipitation of uranyl peroxide, but this can be prevented by adding a catalyst to the solution. A titania sorbent can be used to recover Mo-99 from a highly concentrated uranyl nitrate or uranyl sulfate solution; however, different approaches must be taken to prevent precipitation during Mo-99 production.

Apolipoprotein A-I(Milano) anion exchange chromatography: Self association and adsorption equilibrium

The self-associative properties of apolipoprotein A-I(Milano) (apoA-I(M)) were investigated in relationship to its anion exchange behavior on Q-Sepharose-HP with and without the addition of urea as a denaturant. Self-association was dependent on protein and urea concentration and both influenced interactions of the protein with the chromatographic surface. In the absence of urea, apoA-I(M) was highly associated and existed primarily as a mixture of homodimer, tetramer and hexamer forms. Under these conditions, since the binding strength was greater for the oligomer forms, broad, asymmetrical peaks were obtained in both isocratic and gradient elution. Adding urea depressed self-association and caused unfolding. This resulted in sharper peaks but also decreased the binding strength. Thus, under these conditions chromatographic elution occurred at lower salt concentrations. The adsorption isotherms obtained at high protein loadings were also influenced by self-association and by the varying binding strength of the differently associated and unfolded forms. The isotherms were thus dependent on protein, urea, and salt concentration. Maximum binding capacity was obtained in the absence of urea, where adsorption of oligomers was shown to be dominant. Adding urea reduced the apparent binding capacity and weakened the apparent binding strength. A steric mass action model accounting for competitive binding of the multiple associated forms was used to successfully describe the equilibrium binding behavior using parameters determined from isocratic elution and isotherm experiments.

Phenomena of insulin peak fronting in size exclusion chromatography and strategies to reduce fronting

Insulin peak fronting in size exclusion chromatography (SEC) results in more than 10% yield loss in the production of insulin. The goal of this study is to understand the mechanisms of peak fronting and to develop strategies to reduce fronting and increase insulin yield. Chromatography experiments ruled out pressure surge, viscous fingering, and adsorption as the cause for peak fronting. Theoretical analysis based on a general rate model indicated that reversible dimerization is the major cause for peak fronting and reducing the dimerization equilibrium constant is the most effective method for reducing fronting. Two strategies were developed and tested to reduce the degree of dimer formation. The first strategy was to use 0.1N acetic acid as the presaturant and eluent. The second strategy was to use 0.8 or 2.8N acetic acid in 20vol.% denatured ethanol as the mobile phase. The experimental results showed that both strategies can reduce insulin peak fronting in SEC, maintain desired product purity, and increase insulin yield to higher than 98%.

Estimation of adsorption isotherm parameters with inverse method—Possible problems

In recent years the inverse method (IM) has been frequently applied to estimate of isotherm parameters. The IM has been used for adsorption process modeling for one, two and even three component chromatography. This method requires only a few injections with various sample concentrations, so the solute consumption and time requirements are very modest. The successful estimation of isotherm parameters with IM depends on applied chromatography column model and a numerical method used to solve the model. For HPLC column the classical equilibrium-dispersive (ED) model can be used. This model is solved frequently with very fast Rouchon finite difference method. However, the accuracy of computations with Rouchon method is decreasing with increase of the number of analyzed components. The aim of this work is the comparison of the results obtained with inverse method when ED model was solved with Rouchon or orthogonal collocation on finite element (OCFE) scheme. Assuming that solution of ED model with OCFE method can be regarded as real a solution, it was found that the Rouchon scheme may not give satisfactory results even for column with 10,000 theoretical plates for three component chromatography. Moreover, the optimal conditions for separation, calculated with Rouchon method, can be remarkably different from that obtained with the OCFE method. The next aim of this work is the presentation of Craig method application to estimation of model parameters with IM.

Dynamic sorption of ionizable organic compounds (IOCs) and xylene from water using geomaterial-modified montmorillonite

Adsorption of phenols and xylene onto composite material, Na-montmorillonite, activated carbon, cement and water mixture, 70%, 7%, 7% and 16% (w/w/w/w), respectively, was studied at pH values of 5.15, 4.55, 5.2 and 4.9, respectively, of phenol, 2-CP, 2-NP and xylene. Equilibrium isotherms and fixed-bed column studies were undertaken to evaluate the performance of clay-active coal-coated cement (CACC) in removing phenols from aqueous solution. Investigations revealed CACC to be a very efficient media for the removal of phenols from water. The suitability of the Langmuir adsorption model to the equilibrium data was investigated for all phenols-adsorbent systems. At the maximum sorption capacity of the composite material it was found that the uptake (mg phenols/g) of phenols increased in the order 2-CP>2-NP>phenol approximately m-xylene as do their solubilities. The LUB design approach was used to determine the equivalent length of unused bed. The lower LUB values imply a better utilization of CACC composite. A model, which considered the effect of axial dispersion, was successfully used to describe the fixed-bed operation, the axial dispersion coefficient increased significantly with solubility.

Modeling of the Mass-Transfer Kinetics in Chromatographic Columns Packed with Shell and Pellicular Particles

The equations of the general rate model of chromatography and those of simple models (the POR, equilibrium-dispersive, and transport-dispersive models) are derived for beds packed with shell particles. Shell particles are made of a solid, nonporous core surrounded by a shell of a porous material that has properties similar to those of the fully porous materials conventionally used in HPLC. These equations have no algebraic solutions, but the moments of the peaks eluted under linear conditions can be calculated, affording the HETP equation for these columns. The discussion of the contribution to the HETP of the mass-transfer resistances shows that shell particles exhibit much lower plate heights for large molecular size compounds (e.g., peptides and proteins) than do fully porous particles, this advantage increasing with decreasing thickness of the shell. In contrast, the efficiencies of columns packed with shell particles and with fully porous particles having the same diameters are nearly the same for low molecular weight compounds. In practice, the gain in efficiency due to the use of shell particles to separate high molecular weight compounds does not depend on the thickness of the shell provided that this thickness does not exceed 30-40% of the particle diameter. For larger thicknesses, it decreases with increasing thickness. Shell particles can also be used in preparative chromatography. For compounds that have a high internal mass-transfer resistance, the gain in efficiency compensates the reduction in sample capacity due to the lower volume of porous adsorbent. For proteins like BSA, the production rate could be doubled. The gain decreases with decreasing mass-transfer resistance, e.g., with decreasing molecular weight.

Theoretical analysis of the effects of reversible dimerization in size exclusion chromatography

Reversible dimer formation in size exclusion chromatography (SEC) can cause peak splitting, merging, tailing, and fronting. Such behavior can be predicted by the association rate and the dissociation rate relative to the convection rate. Slow association and dissociation result in separated monomer and dimer peaks. Fast association and slow dissociation result in one single dimer peak. Slow association and fast dissociation result in one single monomer peak. Intermediate association and dissociation result in a merged, broad peak with either fronting when monomers dominate or tailing when dimers dominate. A diagram based on the two relative rates is generated to predict general peak shape and retention behavior in SEC.