Stanley I. Sandler

Insights into the Interplay of Lewis and Brønsted Acid Catalysts in Glucose and Fructose Conversion to 5-(Hydroxymethyl)furfural and Levulinic Acid in Aqueous Media

5-(Hydroxymethyl)furfural (HMF) and levulinic acid production from glucose in a cascade of reactions using a Lewis acid (CrCl3) catalyst together with a Brønsted acid (HCl) catalyst in aqueous media is investigated. It is shown that CrCl3 is an active Lewis acid catalyst in glucose isomerization to fructose, and the combined Lewis and Brønsted acid catalysts perform the isomerization and dehydration/rehydration reactions. A CrCl3 speciation model in conjunction with kinetics results indicates that the hydrolyzed Cr(III) complex [Cr(H2O)5OH](2+) is the most active Cr species in glucose isomerization and probably acts as a Lewis acid-Brønsted base bifunctional site. Extended X-ray absorption fine structure spectroscopy and Car-Parrinello molecular dynamics simulations indicate a strong interaction between the Cr cation and the glucose molecule whereby some water molecules are displaced from the first coordination sphere of Cr by the glucose to enable ring-opening and isomerization of glucose. Additionally, complex interactions between the two catalysts are revealed: Brønsted acidity retards aldose-to-ketose isomerization by decreasing the equilibrium concentration of [Cr(H2O)5OH](2+). In contrast, Lewis acidity increases the overall rate of consumption of fructose and HMF compared to Brønsted acid catalysis by promoting side reactions. Even in the absence of HCl, hydrolysis of Cr(III) decreases the solution pH, and this intrinsic Brønsted acidity drives the dehydration and rehydration reactions. Yields of 46% levulinic acid in a single phase and 59% HMF in a biphasic system have been achieved at moderate temperatures by combining CrCl3 and HCl.

Rapid measurement of protein osmotic second virial coefficients by self-interaction chromatography.

Weak protein interactions are often characterized in terms of the osmotic second virial coefficient (B(22)), which has been shown to correlate with protein phase behavior, such as crystallization. Traditional methods for measuring B(22), such as static light scattering, are too expensive in terms of both time and protein to allow extensive exploration of the effects of solution conditions on B(22). In this work we have measured protein interactions using self-interaction chromatography, in which protein is immobilized on chromatographic particles and the retention of the same protein is measured in isocratic elution. The relative retention of the protein reflects the average protein interactions, which we have related to the second virial coefficient via statistical mechanics. We obtain quantitative agreement between virial coefficients measured by self-interaction chromatography and traditional characterization methods for both lysozyme and chymotrypsinogen over a wide range of pH and ionic strengths, yet self-interaction chromatography requires at least an order of magnitude less time and protein than other methods. The method thus holds significant promise for the characterization of protein interactions requiring only commonly available laboratory equipment, little specialized expertise, and relatively small investments of both time and protein.

An equation of state for the hard-sphere chain fluid: theory and Monte Carlo simulation

Abstract We have developed a modified version of the thermodynamic perturbation theory of Wertheim for the hard-sphere chain fluid by incorporating structural information for the diatomic fluid. Using two explicit expressions for the site—site correlation function at contact for the diatomic fluid, we obtained new equations of state for the hard-sphere chain fluid which are accurate at both low and high densities. We also performed Monte Carlo simulations for a bulk hard-sphere chain fluid, and obtained the compressibility factor using the Nezbedas pressure equation extended to a chain fluid. We found that our results are consistent with the results of Dickman and Hall, but of higher accuracy and cover a wider range of density. By comparing with simulation results, we find that our modified thermodynamic perturbation theory is an accurate and convenient tool which can be useful for more realistic models of chain fluids.

The generalized van der Waals partition function. II: Application to the square-well fluid

Abstract A formulation of the generalized van der Waals partition function derived earlier is used here, together with insights obtained from computer simulation, to develop two new equations of state for the square-well fluid. One of these equations is remarkably simple in form, and leads to compressibility factor, vapor pressure and orthobaric density predictions which are as good as, or better than, those obtained with the much more complicated equations of state which have been proposed in the past for the square-well fluid. Further, using this equation, with square-well parameters obtained from second virial coefficient data, and only one adjustable parameter, remarkably good predictions are obtained for the P-V-T and saturation properties of argon and methane.

The correlation functions of hard‐sphere chain fluids: Comparison of the Wertheim integral equation theory with the Monte Carlo simulation

The correlation functions of homonuclear hard‐sphere chain fluids are studied using the Wertheim integral equation theory for associating fluids and the Monte Carlo simulation method. The molecular model used in the simulations is the freely jointed hard‐sphere chain with spheres that are tangentially connected. In the Wertheim theory, such a chain molecule is described by sticky hard spheres with two independent attraction sites on the surface of each sphere. The OZ‐like equation for this associating fluid is analytically solved using the polymer‐PY closure and by imposing a single bonding condition. By equating the mean chain length of this associating hard sphere fluid to the fixed length of the hard‐sphere chains used in simulation, we find that the correlation functions for the chain fluids are accurately predicted. From the Wertheim theory we also obtain predictions for the overall correlation functions that include intramolecular correlations. In addition, the results for the average intermolecular...

Phase behavior of clathrate hydrates: a model for single and multiple gas component hydrates

Abstract Presented here is a model that accurately predicts equilibrium pressures as a function of temperature of hydrates with CH 4 , C 2 H 6 , C 3 H 8 , N 2 , H 2 , and CO 2 and their mixtures as guests. The model parameters fit to a subset of the equilibrium pressure data for single guest hydrates allow the prediction of phase behavior in mixed guest hydrates. For single guest hydrates, our model improves upon the van der Waals and Platteeuw (vdWP) model with a percent absolute average deviation (%AAD) from all equilibrium pressure data of 5.7% compared to 15.1% for the vdWP model. Predictions of equilibrium pressures for all available mixed guest hydrates result in a 11.6%AAD with our fugacity-based model compared to 18.6% for the vdWP model. Also, our model leads to a prediction of the structure change of the methane–ethane hydrate within 5% of its known equilibrium composition in the vapor phase without any adjustment of its parameters. We have also found that at temperatures above 300 K , double occupancy of nitrogen in the large cavity of structure II hydrate is important for the prediction of accurate equilibrium pressures.

A completely analytic perturbation theory for the square-well fluid of variable well width

We present an analytic equation of state, without any adjustable parameters, for the square-well fluid of variable well width (1 ⩽ λ ⩽ 2) based on perturbation theory using the real expression for the radial distribution function of hard spheres that we have recently developed. This work can be regarded as the analytic counterpart of the numerical perturbation theory of Barker and Henderson. The explicit description of the square-well fluid in closed form allows us to easily assess the accuracy of perturbation theory, particularly for the critical properties and vapour-liquid equilibrium which require the integration of the equation of state. As a test of this equation of state, the real fluids neon, argon and methane are considered. A good correlation is obtained between the new equation of state and experimental pVT data, except near the critical point, and the potential parameters for these fluids obtained from the best fit of our equation of state to experimental data can be used over whole density ra...

Phase behavior of aqueous two-polymer systems

Abstract In this work we consider the thermodynamic description of the liquidliquid phase behavior of dextranpolyethylene glycolwater systems which are of interest for biological separations. In this effort, we use the Flory-Huggins and UNIQUAC models, and develop a new numerical procedure to estimate the interaction parameters. Also, when using interaction parameters for the Flory-Huggins model obtained from osmotic pressure and plait point data, qualitatively reasonable binodal curves were obtained. Due to the asymmetry in the experimental binodal curves for these polymer systems, there is a small difference between the calculated interaction parameters for each of the polymers with water. The location of a binodal curve is found to be sensitively dependent on the interactions between the unlike polymers. Multiple sets of interaction parameters were found for the UNIQUAC model which could describe liquidliquid phase splitting in a reasonable manner. In particular, an intercorrelation was found in which any set of parameters in a broad range could predict the phase behavior equally well. Also, the volume and surface area parameters of the polymers were found to play an important role in determining phase behavior of these polymer systems. The shift of the binodal curve with molecular weight of the polymers was also investigated.

The generalized van der waals partition function. I. basic theory

Abstract Sandler, S.I., 1985. The generalized van der Waals partition function. I. Basic theory. Fluid Phase Equilibria , 19:233-257 In this paper we provide a new derivation of the generalized van der Waals partition function for pure fluids and mixtures, and show how this partition function can be used as a basis for understanding equations of state, their mixing rules, and excess free energy (activity coefficient) models. The results presented here clarify some of the confusion which presently exists in the literature concerning the ramifications of local composition thermodynamic models, and provide the theory for papers to follow which combine the generalized van der Waals partition function and our computer simulation results to obtain new, statistical mechanical-based thermodynamic models.

Linear-nonequilibrium thermodynamics theory for coupled heat and mass transport

Abstract Linear-nonequilibrium thermodynamics (LNET) has been used to express the entropy generation and dissipation functions representing the true forces and flows for heat and mass transport in a multicomponent fluid. These forces and flows are introduced into the phenomenological equations to formulate the coupling phenomenon between heat and mass flows. The degree of the coupling is also discussed. In the literature such coupling has been formulated incompletely and sometimes in a confusing manner. The reason for this is the lack of a proper combination of LNET theory with the phenomenological theory. The LNET theory involves identifying the conjugated flows and forces that are related to each other with the phenomenological coefficients that obey the Onsager relations. In doing so, the theory utilizes the dissipation function or the entropy generation equation derived from the Gibbs relation. This derivation assumes that local thermodynamic equilibrium holds for processes not far away from the equilibrium. With this assumption we have used the phenomenological equations relating the conjugated flows and forces defined by the dissipation function of the irreversible transport and rate process. We have expressed the phenomenological equations with the resistance coefficients that are capable of reflecting the extent of the interactions between heat and mass flows. We call this the dissipation-phenomenological equation (DPE) approach, which leads to correct expression for coupled processes, and for the second law analysis.