Method for efficient recovery of high-purity polycarbonates from electronic waste.

More than one million tons of polycarbonates from waste electrical and electronic equipment are consigned to landfills at an increasing rate of 3-5% per year. Recycling the polymer waste should have a major environmental impact. Pure solvents cannot be used to selectively extract polycarbonates from mixtures of polymers with similar properties. In this study, selective mixed solvents are found using guidelines from Hansen solubility parameters, gradient polymer elution chromatography, and solubility tests. A room-temperature sequential extraction process using two mixed solvents is developed to recover polycarbonates with high yield (>95%) and a similar purity and molecular weight distribution as virgin polycarbonates. The estimated cost of recovery is less than 30% of the cost of producing virgin polycarbonates from petroleum. This method would potentially reduce raw materials from petroleum, use 84% less energy, reduce emission by 1-6 tons of CO2 per ton of polycarbonates, and reduce polymer accumulation in landfills and associated environmental hazards.

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.

Experimental and computational studies of enantioseparation of structurally similar chiral compounds on amylose tris(3,5-dimethylphenylcarbamate).

The enantioseparation of 14 structurally similar chiral solutes, with one or two chiral centers, are studied for a commercially important polysaccharide-based chiral stationary phase, amylose tris(3,5-dimethylphenylcarbamate) (ADMPC). Among these solutes, only two solutes show significant enantioresolutions of 2 to 2.5 in n-hexane/2-propanol (90/10, v/v) at 298 K. The retention factors of the chiral solutes vary significantly from 0.7 to 7.0, and they are compared with those of simpler nonchiral solutes having similar but fewer functional groups. The sorbent-solute H-bonding interactions between the solute functional groups and the polymer C=O and NH functional groups are probed with attenuated total reflection infrared spectroscopy (ATR-IR). The H-bonding interactions of the polymer C=O and NH groups with the solutes result in changes in the IR amide band wavenumbers of ADMPC upon solute adsorption. The nanostructure of an ADMPC cavity and the potential interactions with the chiral solutes are proposed based on the sorbent-solute-solvent HPLC data, the sorbent-solute IR data, and the sorbent-solute molecular dynamics (MD) simulations. The results are consistent with the three point attachment hypothesis and indicate that a significant enantioresolution in ADMPC requires at least three different interaction sites for simultaneous H-bonds and phenyl-phenyl interactions for phenylpropylamine (PPA) and various structurally similar chiral solutes.

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%.

Experimental probing and modeling of key sorbent-solute interactions of norephedrine enantiomers with polysaccharide-based chiral stationary phases.

The key interactions of a chiral solute, norephedrine or 2-amino-1-phenyl-1-propanol (PPA), with three commercially important polysaccharide-based chiral stationary phases, amylose Tris(3,5-dimethylphenylcarbamate) (ADMPC), amylose Tris((S)-alpha-methylbenzylcarbamate) (ASMBC) and cellulose Tris(3,5-dimethylphenylcarbamate) (CDMPC) are studied in detail using different experimental techniques and molecular simulations. The HPLC retention factors of the enantiomers of PPA in n-hexane/2-propanol (90/10, v/v) at 298 K vary significantly with these sorbents. The enantioselectivities of -PPA versus +PPA are 2.4, 1.0, and 0.8 (reversal in the elution order), respectively. The observed changes in the wavenumbers and the intensities of the amide bands of these polymers in the attenuated total reflection-infrared spectroscopy (ATR-IR) spectra upon absorption of each enantiomer are different. The IR wavenumbers, and the H-bonding interaction energies of the polymer side chains with each enantiomer (polymer-solute) in four different binding configurations are estimated and ranked using the density functional theory (the DFT/B3LYP/6-311+g(d,p) level of theory). X-ray diffraction (XRD) results show that the polymer crystallinity increases significantly upon absorption of each enantiomer. The helical pitches and the inter-rod packing for these polymers are inferred from the XRD results and incorporated into the molecular dynamics (MD) simulations. The elution orders predicted for the enantiomers of PPA using MD simulations of the polymer-PPA binary systems are consistent with the chromatography results. The enantioselectivity observed in ADMPC is hypothesized to be due to having three simultaneous interactions (two H-bond and one pi-pi) of the polymer with -PPA versus two interactions (one H-bond and one pi-pi) with +PPA.

Effect of the solute molecular structure on its enantioresolution on cellulose tris(3,5-dimethylphenylcarbamate).

The effects of the molecular structures for 13 structurally similar chiral solutes on their HPLC retention and enantioresolutions on a commercially important polysaccharide-based chiral stationary phase, cellulose tris(3,5-dimethylphenylcarbamate) (CDMPC) are studied. Among these 13 solutes, only methyl ephedrine (MEph) shows significant enantioresolution. The retention factors of these chiral solutes vary significantly from 0.7 to 3.2 in n-hexane/2-propanol (90/10, v/v) at 298 K. The retention factors of some simpler non-chiral solutes having similar but fewer functional groups than their chiral counterparts are also studied under the same conditions and are compared to those of the chiral solutes. The H-bonding interactions between the functional groups of the solute and the C=O and NH functional groups of the polymer are probed with attenuated total reflection-infrared spectroscopy (ATR-IR) for the polymer, for binary sorbent-solute systems. The CDMPC IR amide band wavenumbers change significantly, indicating H-bonding interactions of the polymer C=O and NH groups with the solutes. The elution orders predicted for the enantiomers of these chiral solutes using molecular dynamics (MD) simulations of the polymer-solute binary systems are consistent with the HPLC results. The CDMPC cavity nano-structure and the potential interactions with chiral solutes are proposed based on HPLC data, IR data, and the simulations. The results are consistent with the three-point attachment model and support the hypothesis that significant enantioresolution requires at least three different synergistic interactions which can be a combination of steric hindrance, H-bonding, or pi-pi interactions.

Constant-pattern design method for the separation of ternary mixtures of rare earth elements using ligand-assisted displacement chromatography.

A constant-pattern design method for separating ternary mixtures using ligand-assisted displacement chromatography was developed for non-ideal systems. The general correlation for the minimum column length required to achieve the constant-pattern state for binary separations from our previous study was extended to ternary separations. Additionally, an equation for the yield of a target component as a function of key dimensionless groups was derived based on the constant-pattern mass transfer zone lengths. The column length and operating velocity solved from the two equations ensured the yields and the constant-pattern state for the target components. A selectivity weighted composition factor was developed to allow the design method to specify a minimum target yield for one or multiple components. The design method was verified using simulations and experiments for different targeted yields (70-95%), ligand concentrations (0.03-0.06 M), and feed compositions (1/12-5/6). The targeted yields were achieved or exceeded in all cases tested. The minimum column length required to achieve a constant pattern-state and the productivity of LAD are limited by the lowest selectivity or by a minority component with a low concentration in the feed, even when it does not have the lowest selectivity. Sacrificing the yields of minor components can increase the total productivity significantly. The productivities achieved using this design method are 839 times higher than literature results for ternary separations with the same purity and similar yields.

Key parameters controlling the development of constant-pattern isotachic trains of two rare earth elements in ligand-assisted displacement chromatography.

Ligand-assisted displacement chromatography (LAD) has been developed for separating rare earth elements since the 1950's. Isotachic displacement trains, which are similar to those in conventional displacement chromatography, were reported previously. However, there has been no general theory delineating the conditions required to form constant-pattern displacement trains for non-ideal systems (or systems with significant mass transfer resistance). The constant-pattern state is critical for obtaining pure products with high yield and high productivity. Without theoretical guidance, all the previous studies found the constant-pattern state by experimental trial and error, which was time consuming and costly. In this study, an efficient rate model and simulations of LAD were developed and verified with experimental data for non-ideal systems. Verified simulations were used to understand the mechanisms of separations and the transition from the transient state to the constant-pattern state. The key dimensionless factors affecting the transition for binary non-ideal systems were identified. Dimensionless groups were developed to reduce the number of variables. Simulations were used to find the transition points fromthe transient state to the constant-pattern state, which indicates the minimum dimensionless column lengths in the multi-parameter space. Strategic combination of the key dimensionless groups allows the minimum dimensionless column lengths to correlate with the combined groups in a two-dimensional diagram (or a map). The correlation curve divides the multi-dimensional space into the transient region and the constant-pattern region. The correlation was further verified with five sets of experiments. It can be used to find, without process simulations or experiments, the minimum column lengths for developing constant-pattern isotachic trains for non-ideal systems, which is useful for designing efficient ligand-assisted displacement chromatography at any scale.

Speedy standing wave design, optimization, and scaling rules of simulated moving bed systems with linear isotherms.

Simulated Moving Bed (SMB) systems with linear adsorption isotherms have been used for many different separations, including large-scale sugar separations. While SMBs are much more efficient than batch operations, they are not widely used for large-scale production because there are two key barriers. The methods for design, optimization, and scale-up are complex for non-ideal systems. The Speedy Standing Wave Design (SSWD) is developed here to reduce these barriers. The productivity (PR) and the solvent efficiency (F/D) are explicitly related to seven material properties and 13 design parameters. For diffusion-controlled systems, the maximum PR or F/D is controlled by two key dimensionless material properties, the selectivity (α) and the effective diffusivity ratio (η), and two key dimensionless design parameters, the ratios of step time/diffusion time and pressure-limited convection time/diffusion time. The optimum column configuration for maximum PR or F/D is controlled by the weighted diffusivity ratio (η/α2). In general, high α and low η/α2 favor high PR and F/D. The productivity is proportional to the ratio of the feed concentration to the diffusion time. Small particles and high diffusivities favor high productivity, but do not affect solvent efficiency. Simple scaling rules are derived from the two key dimensionless design parameters. The separation of acetic acid from glucose in biomass hydrolysate is used as an example to show how the productivity and the solvent efficiency are affected by the key dimensionless material and design parameters. Ten design parameters are optimized for maximum PR or minimum cost in one minute on a laptop computer. If the material properties are the same for different particle sizes and the dimensionless groups are kept constant, then lab-scale testing consumes less materials and can be done four times faster using particles with half the particle size.

Improvement of the performances of a tandem simulated moving bed chromatography by controlling the yield level of a key product of the first simulated moving bed unit.

One of the trustworthy processes for ternary separation is a tandem simulated moving bed (SMB) process, which consists of two subordinate four-zone SMB units (Ring I and Ring II). To take full advantage of a tandem SMB as a means of recovering all three products with high purities and high economical efficiency, it is important to understand how the separation condition in Ring II is affected by that in Ring I, and further to reflect such point in the stage of designing a tandem SMB. In regard to such issue, it was clarified in this study that the Ring I factors affecting the Ring II condition could be represented by the yield level of a key product of Ring I (YkeyRingI). As the YkeyRingI level became higher, the amount of the Ring I key-product that was reloaded into Ring II was reduced, which affected favorably the Ring II separation condition. On the other hand, the higher YkeyRingI level caused a larger dilution for the stream from Ring I to Ring II, which affected adversely the Ring II separation condition. As a result, a minimum in the desorbent usage of a tandem SMB occurred at the YkeyRingI level where the two aforementioned factors could be balanced with each other. If such an optimal YkeyRingI level was adopted, the desorbent usage could be reduced by up to 25%. It was also found that as the throughput of a tandem SMB became higher, the factor related to the migration of the Ring I key-product into Ring II was more influential in the performances of a tandem SMB than the factor related to the dilution of the stream from Ring I to Ring II.

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.

Design of simulated moving bed for separation of fumaric acid with a little fronting phenomenon.

The production of fumaric acid through a biotechnological pathway has grown in importance because of its potential value in related industries. This has sparked an interest in developing an economically-efficient process for separation of fumaric acid (product of interest) from acetic acid (by-product). This study aimed to develop a simulated moving bed (SMB) chromatographic process for such separation in a systematic way. As a first step for this work, commercially available adsorbents were screened for their applicability to the considered separation, which revealed that an Amberchrom-CG71C resin had a sufficient potential to become an adsorbent of the targeted SMB. Using this adsorbent, the intrinsic parameters of fumaric and acetic acids were determined and then applied to optimizing the SMB process under consideration. The optimized SMB process was tested experimentally, from which the yield of fumaric-acid product was found to become lower than expected in the design. An investigation about the reason for such problem revealed that it was attributed to a fronting phenomenon occurring in the solute band of fumaric acid. To resolve this issue, the extent of the fronting was evaluated quantitatively using an experimental axial dispersion coefficient for fumaric acid, which was then considered in the design of the SMB of interest. The SMB experimental results showed that the SMB design based on the consideration of the fumaric-acid fronting could guarantee the attainment of both high purity (>99%) and high yield (>99%) for fumaric-acid product under the desorbent consumption of 2.6 and the throughput of 0.36L/L/h.

Standing wave design and optimization of a simulated moving bed chromatography for separation of xylobiose and xylose under the constraints on product concentration and pressure drop.

The feasibility of a simulated moving bed (SMB) technology for the continuous separation of high-purity xylobiose (X2) from the output of a ß-xylosidase X1→X2 reaction has recently been confirmed. To ensure high economical efficiency of the X2 production method based on the use of xylose (X1) as a starting material, it is essential to accomplish the comprehensive optimization of the X2-separation SMB process in such a way that its X2 productivity can be maximized while maintaining the X2 product concentration from the SMB as high as possible in consideration of a subsequent lyophilization step. To address this issue, a suitable SMB optimization tool for the aforementioned task was prepared based on standing wave design theory. The prepared tool was then used to optimize the SMB operation parameters, column configuration, total column number, adsorbent particle size, and X2 yield while meeting the constraints on X2 purity, X2 product concentration, and pressure drop. The results showed that the use of a larger particle size caused the productivity to be limited by the constraint on X2 product concentration, and a maximum productivity was attained by choosing the particle size such that the effect of the X2-concentration limiting factor could be balanced with that of pressure-drop limiting factor. If the target level of X2 product concentration was elevated, higher productivity could be achieved by decreasing particle size, raising the level of X2 yield, and increasing the column number in the zones containing the front and rear of X2 solute band.

Direct probing of sorbent-solvent interactions for amylose tris(3,5-dimethylphenylcarbamate) using infrared spectroscopy, X-ray diffraction, solid-state NMR, and DFT modeling.

The sorbent-solvent interactions for amylose tris(3, 5-dimethylphenylcarbamate) (ADMPC) with five commonly used solvents, hexane, methanol, ethanol, 2-propanol (IPA), and acetonitrile (ACN), are studied using attenuated total reflection infrared spectroscopy (ATR-IR) of thin sorbent films, X-ray diffraction (XRD) of thin films, (13)C cross polarization/magic angle spinning (CP/MAS) and MAS solid state NMR of polymer-coated silica beads (commercially termed "Chiralpak AD"), and DFT modeling. The ADMPC-polymer-coated silica beads are used commercially for analytical and preparative scale separations of chiral enantiomers. The polymer forms helical rods with intra- and inter-rod hydrogen bonds (H-bonds). There are various nm-sized cavities formed between the polymer side-chains and rods. The changes in the H-bonding states of the C=O and NH groups of the polymer upon absorption of each of the five solvents at 25 degrees C are determined with ATR-IR. The IR wavenumbers, the H-bonding interaction energies, and the H-bonding distances of the polymer side-chains with each of the solvent molecules are predicted using the DFT/B3LYP/6-311+g(d,p) level of theory. The changes in the polymer crystallinity upon absorption of each solvent are characterized with XRD. The changes in the polymer crystallinity and the H-bonding states of C=O groups are also probed with (13)C CP/MAS solid-state NMR. The changes in the polymer side-chain mobility are detected using (13)C MAS solid-state NMR. The H-bonding states of the polymer change upon absorption of each polar solvent and usually result in an increase in the polymer crystallinity and the side-chain mobility. The polymer rods are reorganized upon solvent absorption, and the distance between the rods increases with the increase in the solvent molecular size. These results have implications for understanding the role of the solvent in modifying the structure and behavior of the polymer sorbents.

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.

In situ probing of insulin aggregation in chromatography effluents with spectroturbidimetry.

Probing protein aggregation in situ is quite important for analyzing and developing chromatographic protein purification processes. A spectroturbidimetry method with a photodiode array detector is developed and tested for probing insulin aggregation in solution and determining the aggregation number, n(m). All aggregates examined are in the Rayleigh light scattering regime, where the turbidity between 400 and 350 nm is proportional to lambda(-4). Insulin at 25 degrees C in 3.5 N acetic acid is mainly monomeric (non-aggregated). At 25 degrees C and lower acetic acid concentrations, from 0.1 to 1 N, the average insulin aggregation number n(m) ranges from 2.9 to 1.6. Aggregates, with n(m) = 2-3, are found in 2.6 N acetic acid with 20 vol% acetonitrile. In 0.8 N acetic acid with 20 vol% denatured ethanol, n(m) = 1.2. At 4 degrees C, as acetic acid concentration decreases from 3.5 to 0.1 N, n(m) decreases from 2.4 to 1.8. In 2.8 N acetic acid with 20 vol% denatured ethanol at 4 degrees C, insulin exists mainly in monomer form. In situ probing of size exclusion chromatography, SEC, effluents in 3.5 N acetic acid at 4 degrees C shows n(m) = 1.6 at the fronting portion (a mixture of monomers and dimers or other oligomers) and n(m) = 1.1 (mostly monomers) at the tailing portion of the main peak. In another example, for LysPro-insulin in reversed phase chromatography at 4 degrees C, complex elution patterns and broad peaks are due to substantial aggregation. For a linear gradient of acetonitrile from 10 to 60 vol% at 4 degrees C, n(m) ranges from 2.2 to 12, in order of elution. For a linear gradient of ethanol from 30 to 50 vol% at 4 degrees C, n(m) ranges from 14 to 27, in order of elution. Analytical HPLC results at 25 degrees C imply that the aggregates are reversible.

Continuous recovery of valine in a model mixture of amino acids and salt from Corynebacterium bacteria fermentation using a simulated moving bed chromatography.

The economical efficiency of valine production in related industries is largely affected by the performance of a valine separation process, in which valine is to be separated from leucine, alanine, and ammonium sulfate. Such separation is currently handled by a batch-mode hybrid process based on ion-exchange and crystallization schemes. To make a substantial improvement in the economical efficiency of an industrial valine production, such a batch-mode process based on two different separation schemes needs to be converted into a continuous-mode separation process based on a single separation scheme. To address this issue, a simulated moving bed (SMB) technology was applied in this study to the development of a continuous-mode valine-separation chromatographic process with uniformity in adsorbent and liquid phases. It was first found that a Chromalite-PCG600C resin could be eligible for the adsorbent of such process, particularly in an industrial scale. The intrinsic parameters of each component on the Chromalite-PCG600C adsorbent were determined and then utilized in selecting a proper set of configurations for SMB units, columns, and ports, under which the SMB operating parameters were optimized with a genetic algorithm. Finally, the optimized SMB based on the selected configurations was tested experimentally, which confirmed its effectiveness in continuous separation of valine from leucine, alanine, ammonium sulfate with high purity, high yield, high throughput, and high valine product concentration. It is thus expected that the developed SMB process in this study will be able to serve as one of the trustworthy ways of improving the economical efficiency of an industrial valine production process.

Highly efficient recovery of xylobiose from xylooligosaccharides using a simulated moving bed method.

Xylobiose (X2), which is currently available from xylooligosaccharides (XOS), has been reported to have outstanding prebiotic function and to be highly suitable for application in food industries. This has sparked an interest in the economical production of X2 of high purity (> 99%) in food and prebiotic industries. To address such issue, we developed a highly-efficient chromatographic method for the recovery of X2 from XOS with high purity and high recovery. As a first step for this work, an eligible adsorbent for a large-scale separation between X2 and other XOS components was selected. For the selected adsorbent, a single-column experiment was carried out to determine the intrinsic parameters of all the XOS components, which were then used in the optimal design of the continuous X2-recovery process based on a simulated moving bed (SMB) chromatographic method. Finally, the performance of the designed X2-recovery SMB process was verified by the relevant SMB experiments, which confirmed that the developed process in this study could recover X2 from XOS with the purity of 99.5% and the recovery of 92.3% on a continuous-separation mode. The results of this study will be useful in enabling the economical production of high-purity X2 on a large scale.