Roger D. Hester

Deconvolution of overlapping chromatographic peaks using constrained non-linear optimization

Abstract Non-linear regression involving Gaussian, modified Gaussian or Weibull functions is currently used for deconvoluting fused chromatograms. In this paper, we report that deconvolution of fused chromatograms is a problem in constrained non-linear optimization and not an unconstrained problem as assumed by previous researchers. A modified version of the generalized exponential function is shown to fit chromatographic peaks using the Box-Complex method for constrained optimization. Previously reported problems of false fits do not occur with this method. Several deconvolutios on real size exclusion chromatographic data are shown to demonstrate the power of the technique.

Rheology of waterborne coatings

SummaryThe rheology of a latex paint must be controlled to produce an acceptable coating. Conditions vary as a paint is sequentially taken from storage, applied to a substrate and then cured in place. As shown byTable 1, desirable films are produced only when paint viscosities and yield points are controlled at each process step. Thus, an understanding and control of paint rheology are essential if high quality coatings are to be produced from latex paints.

Structural Characterization and Solution Properties of a Galacturonate Polysaccharide Derived from Aloe vera Capable of in Situ Gelation

A series of highly purified galacturonate polysaccharides have been extracted from the Aloe vera plant and analyzed in terms of chemical composition and molecular weight. This Aloe vera polysaccharide (AvP) has been found to exist as a high molecular weight species and possess a unique chemical composition, including a high galacturonic acid (GalA) content and low degree of methyl ester substitution. These factors facilitate gel formation upon exposure to low concentrations of calcium ions, leading to potential application in formulations designed for in situ nasal or subcutaneous protein delivery. Thorough examination of classic dilute solution properties, the [eta]-M(w), and R(g)-M(w) relationships, persistence length (L(p)), and inherent chain stiffness (B parameter), indicate an expanded random coil in aqueous salt solutions. The critical concentration for transition from dilute to concentrated solution, C(e), was determined by measuring both the zero shear viscosity (eta(o)) and fluorescence emission of the probe molecule 1,8-anilino-1-naphthalene sulfonic acid (1,8-ANS) as a function of polymer concentration. Examination of zeta potential and C(e) as a function of ionic strength indicates that the shift in C(e) from 0.60 to 0.30 wt % is related to an increased occurrence of intermolecular interactions at high salt concentrations. Additionally, dynamic rheology data are presented highlighting the ability of AvP to form gels at low polymer and calcium ion concentrations, exemplifying the technological potential of this polysaccharide for in situ drug delivery.

Concentrated Acid Conversion of Pine Softwood to Sugars. Part I: Use of a Twin-Screw Reactor for Hydrolysis Pretreatment

The first stage of a two-step concentrated sulfuric acid process that converts softwood sawdust to sugars has been explored. The research focuses on the ability of an in-house custom fabricated corotating twin-screw reactor (TSR) to effectively break down and solubilize crystalline cellulose into low molecular weight carbohydrates. Based on design of experiment (DOE) screening results, a four-level, two-factor experimental model building DOE was undertaken. Solid sawdust conversion to liquid, screw torque, and TSR exit pressure were measured or recorded at each experimental condition to yield percent conversion of solids, processed material viscosity, and material energy requirements. Thereafter, model quadratic equations were fitted to the experimental data and found to be statistically significant. Based on data obtained in the DOE the process was optimized to establish a base case operating condition. The acid-treated product made at base case twin-screw operating conditions showed a 38.2% conversion of dry sawdust solids to soluble liquids. The dry solids conversion reduced 73.8% of all hemicellulose and 44.4% of all cellulose to soluble monomers and oligosaccharides.

CONTINUOUS ION-EXCLUSION CHROMATOGRAPHY SYSTEM FOR ACID / SUGAR SEPARATION

ABSTRACT A simulated moving bed ion exclusion chromatography system was constructed for the continuous separation of the components in an aqueous feed solution of sucrose and sulfuric acid. A system of 18 columns was arrayed about a central manifold system. Each column was packed with approximately 820 mL of porous cationic exchange resin. The system was designed for the flexibility to use fluid recycle loops and unrestricted placement of all inlet and outlet streams. Monitoring and control functions were performed using a Camile 2000 process controller integrated with a custom-built control computer. The aqueous feed solution, usually containing 10 wt.% sucrose and 10 wt.% sulfuric acid, was generally introduced into the system at a rate of roughly 2 L/hr. Approximately 4 L/hr of water was used to elute materials through the separation system. After optimization, the separation system allowed greater than 95% recovery of the feed sucrose in an exit stream containing 8.8 wt.% sucrose and 98% recovery of t...

CONCENTRATED ACID CONVERSION OF PINE SAWDUST TO SUGARS. PART II: HIGH-TEMPERATURE BATCH REACTOR KINETICS OF PRETREATED PINE SAWDUST

A study of high-temperature, concentrated-acid hydrolysis kinetics was undertaken for pretreated pine utilizing a corotating twin-screw extruder reactor. Five different acid concentrations were prepared ranging from 5 to 30 wt.% acid. These solutions were subjected to high-temperature acid hydrolysis at 110°, 120°, and 130°C using a custom-fabricated zirconium batch reactor. A number of nonlinear and linear regression analyses were undertaken so that the concentration of less resistant cellulose, resistant cellulose, glucose, and decomposition products could be obtained as a function of time, temperature, and acid concentration. Application of the kinetic rate constants obtained from the static batch reactor hydrolysis studies demonstrates that more than 50% of the theoretical glucose available in the pine sawdust can be obtained in roughly 25 minutes and 41% of the theoretical glucose available can be achieved in as little as 3 minutes. Further analysis highlights the importance of the pretreatment technique in achieving significant quantities of theoretical glucose in a short high-temperature reaction time.

Acid/Sugar Separation Using Ion Exclusion Resins: A Process Analysis and Design

Abstract The economic feasibility of using acid hydrolysis to convert agricultural waste products, such as corn stovers, to alcohol is very dependent upon developing a cost effective sulfuric acidglucose sugar separation process. Presently, an acid/sugar stream from sulfuric acid hydrolysis of cellulose is treated with lime to precipitate the acid as gypsum. This technique not only consumes acid and lime, but also generates waste gypsum that is sent to a landfill. An ion exclusion process to perform acid/sugar separation has been designed using standard resins. Economic analysis based on a process computer model indicates that ion exclusion is 40 % less costly than a lime precipitation process.

DEVELOPMENT AND MODELING OF A CONTINUOUS SIMULATED MOVING BED ION EXCLUSION PROCESS FOR THE SEPARATION OF ACID AND SUGAR

The emission of large quantities of the greenhouse gas carbon dioxide into the atmosphere, as well as our increasing dependence on foreign oil supplies and the need to stimulate the lagging farm economy, has prompted research in the production of renewable liquid fuels from lignocellulosic materials. Acid hydrolysis of the cellulosic fraction of these materials into sugars that can be fermented to ethanol is one option. In support of this approach, a simulated moving bed ion exclusion chromatography system was constructed for the continuous separation of the product sugars from the acid used to effect hydrolysis. A numerical simulation model of the process is presented here. Our system consisted of 4 zones of 18 resin-packed columns, each approximately 820 mL in size, arrayed about a central manifold system using solenoid valves to control fluid flow. The model is based upon experimental data from the system arrayed with 9 doubled and 18 single columns. The numerical simulation model was used in conjunction with statistical experimental design techniques to probe the optimum operating conditions: the selection of the simulated flow rate, the number of columns needed in each zone and the appropriate number of columns in the system as a whole. A development facility more than 10-times the current system size is being pursued.

Low-shear-rate capillary viscometer for polymer solution intrinsic viscosity determination at varying temperatures

A low-shear capillary viscometer has been designed, constructed, and used to measure polymer solution intrinsic viscosities over temperatures ranging from 10 to 75 °C. The instrument is capable of detecting the small shear stress forces produced when low-viscosity fluids are subjected to very low-shear rates. Instrument performance and sensitivity were evaluated using deionized water at temperatures between 10 and 75 °C. The measured water viscosity values differed from the literature values by less than 1%. The viscometer was also used to determine that the intrinsic viscosity of a poly(acrylamide) aqueous solution at 29 °C was 17.7 dL/g. This value was in agreement with the value obtained using a Contraves Low-Shear 30 cup and bob rheometer, 17.9 dL/g.

Synthetic Random and Graft Copolymers for Utilization in Enhanced Oil Recovery—Synthesis and Rheology

Polyelectrolyte and non-polyelectrolyte acrylamide random copolymers and graft copolymers of dextran with acrylamide were synthesized to evaluate the effects of polymer composition and structure on viscosity modification and solution behavior in water and brine. Polymer solution rheological behavior and precipitation properties were measured.