William M. Clark

Protein adsorption and fouling in ceramic ultrafiltration membranes

Abstract The adsorption of proteins to membrane surfaces can lead to the formation of a fouling layer, which drastically reduces permeate flux and represents a serious impediment to efficient ultrafiltration operations. In this work, the factors influencing permeate flux, adsorption and fouling during crossflow ultrafiltration of bovine serum albumin using microporous alumina membranes with mean pore diameters of 40, 350 and 1000 A have been examined. p]In general, the permeate flux was observed to be a function of concentration, transmembrane pressure and crossflow velocity as described by classical gel polarization theory. For protein concentrations above 1 g/l, solute rejection was nearly complete even for the 1000 A membranes. At low solute concentrations, rejection increased with decreasing pore size and increasing crossflow velocity. p]Studies of the flux and rejection dependence on pH, solute concentration, ionic strength, membrane pore size and cleaning procedure, coupled with adsorption studies, indicated that adsorption-related pore plugging plays a significant role in the two larger pore size membranes.

Evaluation of a spiral curriculum for engineering

This paper discusses results of the first two offerings of an experimental and innovative first-year chemical engineering curriculum. The curriculum is project-based in that it emphasizes learning through engagement in open-ended projects from early in the curriculum. It is spiral in that it revisits concepts periodically with increasing sophistication throughout the curriculum. The curriculum is intended to increase technical proficiency, communication and teamwork skills, and identification with chemical engineering as a major and profession. This paper reports results attained through comparison of students from experimental and traditional course sequences with regard to these objectives.

Two-Phase Electrophoresis of Proteins

Abstract Proteins have been directed into either the top or bottom phase of a polyethylene glycol/dextran aqueous two-phase system by applying an electric field perpendicular to the phase interface. Protein migration across the interface was manipulated by varying polarity, pH, electrophoresis time, field strength, and phase volume ratio. Mixtures of hemoglobin and albumin were separated by operating between isoelectric points and directing oppositely charged proteins into separate phases. Applying 50 V/cm for 2 hours to 58 mL of an equal phase volume two-phase system containing 0.2 g/L of each protein at pH 6 resulted in a bottom phase containing 99% of the hemoglobin and a top phase containing 95% of the albumin. This represents a significant improvement over the separation obtained either by partitioning in the same two-phase system with no applied field or by electrophoresis under the same conditions in homogeneous buffer. The two-phase system divides the electrophoresis device into two distinct regio...

Biodiesel transesterification kinetics monitored by pH measurement

Quantification of a pH change that was observed over the course of the transesterification reaction that converts vegetable oil to biodiesel may provide a simple method to monitor the reaction. Transesterification of canola oil at 6:1 methanol to oil ratio with 0.5 wt.% KOH as catalyst was studied at 25, 35, and 45 °C. Reaction conversion was correlated to pH measurements and the results were shown to be in agreement with an independent measure of conversion using an enzymatic assay for glycerol. Rate constants obtained from these measurements are consistent with those in the literature. The measured pH change appears to be related to dilution of OH(-) ions as the oil is converted to products rather than to depletion of OH(-) due to reaction.

Affinity Partitioning and Its Potential in Biotechnology

Abstract The affinity partitioning technique and its applications to biotechnological separations are reviewed. In spite of the great potential for large-scale continuous processing and the wide success in laboratory separations offered by the technique, relatively few reports of biotechnological applications have been made. This underutilization is attributed in part to the lack of design criteria for establishing and optimizing partitioning systems. A first step toward developing a thermodynamically based design model for affinity partitioning, based on the incorporation of a Gibbs energy model for phase equilibria in polymer solutions into a separate theory accounting for the affinity effect, is presented.

β‐Lactamase Recovery from E. coli Cell Lysate via Two‐Phase Electrophoresis

β‐Lactamase was recovered from Escherichia coli cell lysate by a novel cell debris removal method using two‐phase electrophoresis. The cells were harvested by centrifugation after fermentation, resuspended in a low ionic strength electrophoresis buffer, lysed, and combined with a poly(ethylene glycol)/dextran aqueous two‐phase system in the same buffer. The cell lysate was subjected to a 40 V/cm electric field oriented perpendicular to the phase interface for 90 min. Experiments were conducted both with and without a nucleic acid precipitation step using poly(ethylene imine) (PEI). For PEI‐treated lysate at pH 5, the positively charged β‐lactamase was directed to the upper phase, while negatively charged contaminants (including cell debris, nucleic acid/PEI precipitates, and negatively charged proteins) were directed to the lower phase with the applied field. β‐Lactamase yield in the upper phase was 81%, while cell debris and nucleic acids partitioned almost exclusively to the lower phase. For untreated lysate, β‐lactamase did not move in the electric field due to strong interaction with nucleic acids in solution.

Protein adsorption and fouling of ceramic membranes as measured by scanning electron microscopy with digital X-ray mapping

A technique for studying fouling in ceramic membranes using the energy dispersive x-ray spectroscopy capability of an electron microscope is described. The location and amount of foulant within the membrane are presented on a digital x-ray map showing elements constituent to or stained on the foulant. Fouling of alumina membranes during filtration of the protein hemoglobin has been studied as a function of filtration time, pH, and membrane pore size. After each filtration run, the protein within a piece of the membrane was stained with phosphotungstic acid and located on a digital map of either phosphorus or tungsten. For a 0.2 μm pore size membrane, time dependent fouling was observed consistent with an observed flux decline within the first few minutes of filtration. A pH dependence was also observed indicating much greater fouling at pH 6.9 near the protein isoelectric point than at pH 8.5. This observation is consistent with pH dependent adsorption, flux, and rejection studies. No internal fouling was...

An integrated, project-based, spiral curriculum for the first year of chemical engineering

Summary form only given. The authors developed a project-based, spiral curriculum for chemical engineering, beginning with the sophomore year. The curriculum addresses problems in the current state of engineering education, such as lack of student motivation, poor retention, segmented learning, lack of integration and the need to deliver cost effective technical education to a student audience of diverse backgrounds and learning styles. The spiral curriculum was well received by students in the initial offering during the 1997-98 academic year.

Adsorption of Proteins and Antibiotics on Porous Alumina Membranes

Abstract Adsorption of proteins and antibiotics within porous membranes can adversely affect membrane performance during recovery of these products using filtration. The adsorption of two proteins, bovine serum albumin and hemoglobin, and an antibiotic, tetracycline, on alumina membranes has been investigated. Protein adsorption and flux during filtration were observed to be pH dependent with maximum adsorption and minimum flux near the protein isoelectric points. Energy dispersive spectroscopy was used to locate and quantify adsorbed proteins within membrane cross sections after filtration. The pH dependence of adsorption was modeled by including the effects of protein-protein and protein-membrane charge interactions in the random sequential adsorption model.

Work in progress - connecting laboratory experiments to theory through simulation

We are using COMSOL Multiphysicstrade, a commercial finite element modeling software package, to develop simulations of equipment in our unit operations laboratory including a heat exchanger, a gas permeation membrane, and a fluid flow experiment. Our hypothesis is that computer simulations showing the solutions to the differential equations that govern the fluid flow, heat transfer, and mass transfer within the equipment will solidify the link between experiment and theory and provide improved learning. Students in one lab section who used the simulations were compared to those in a control section who did not. A diagnostic quiz given before and after each lab provided a quantitative measure of improvement in learning via the lab experience for both groups. Content analysis of written and oral reports was used to measure any difference in higher level thinking demonstrated by the two groups. Student attitudes towards the simulations were assessed by surveys and end-of-course evaluations. Results so far, in the second year of a three-year project, indicate improvements in student satisfaction and learning but little change in critical thinking that can be attributed to the simulations.