David J. Dixon

Polymeric Microspheres Prepared by Spraying into Compressed Carbon Dioxide

AbstractPurpose. The objective was to prepare polymeric microparticles by atomizing organic polymer solutions into a spray chamber containing compressed CO2 (PCA-process) and to study the influence of various process parameters on their morphological characteristics. Methods. The swelling of various pharmaceutically acceptable polymers [ethyl cellulose, poly(methyl methacrylate), poly(ε-caprolactone), poly(dl-lactide), poly(l-lactide) and poly(dl-lactide-glycolide) copolymers] in CO2 was investigated in order to find polymers which did not agglomerate during the spraying process. Poly(l-lactide) (L-PLA) microparticles were prepared by spraying the organic polymer solution into CO2 in a specially designed spraying apparatus. The effect of various process (pressure and temperature of the CO2 phase, flow rate) and formulation (polymer concentration) variables on the morphology and particle size of L-PLA-microparticles was investigated. Results. Polymers with low glass transition temperatures agglomerated even at low temperatures. The formation of microparticles was favored at moderate temperatures, low polymer concentrations, high pressures and high flow rates of CO2. High polymer concentrations and low flow rates resulted in the formation of polymeric fibers. Colloidal L-PLA particles could also be prepared with this technique in a surfactant-free environment. Initial studies on the microencapsulation of drugs resulted in low encapsulation efficiencies. Conclusions. The PCA method is a promising technique for the preparation of drug-containing microparticles. Potential advantages of this method include the flexibility of preparing microparticles of different size and morphology, the elimination of surfactants, the minimization of residual organic solvents, low to moderate processing temperatures and the potential for scale-up.

Microcellular microspheres and microballoons by precipitation with a vapour-liquid compressed fluid antisolvent

Abstract A new type of precipitation with a compressed fluid antisolvent (PCA) is demonstrated for the formation of porous polymeric microspheres and microballoons (hollow microspheres). The antisolvent is composed of pure saturated vapour over saturated liquid CO2. A polystyrene (PS) in toluene solution is sprayed through a capillary into CO2 vapour to form droplets, which fall into liquid CO2 where they are rapidly dried and vitrified. Both the thickness and porosity of the microcellular shells can be controlled by changing the initial solution composition. The thickness is inversely proportional to the initial PS concentration. As the concentration is increased there is a transition from porous microballoons to porous microspheres. The cell sizes and surface areas of the microspheres are approximately 1–20 μm and 3–40 m2g−1, respectively. The mass transfer pathway may be altered by addition of CO2 to the polymer solution before spraying, resulting in greater and more uniform porosity. Compared with methanol as an antisolvent, CO2 produces more porous and spherical microspheres, with 7–14 times faster precipitation.

Tri-n-butylphosphate/CO2 and acetone/CO2 phase behaviors and utilities in capillary supercritical-fluid chromatography

Abstract Because the phase behavior of the mobile phase must be known before conclusions from supercritical-fluid chromatography (SFC) can be considered reliable, the phase behaviors of tri- n -butylphos-phate/C0 2 and acetone/CO 2 were thoroughly determined in a variable-volume view cell at conditions applicable to SFC (0–20 mol % modifier, 25–140 °C, and 80–415 atm). The chromatographic utilities of the binary fluids were determined with test compounds (condensed tannins and steroids). Although the UV-absorbance detector base-line rise was severe with acetone/CO 2 , chromatographic performance was not compromised. Standard base-line correction methods were used to produce conventional-looking chromatograms. The chromatographic performance with tri- n -butylphosphate/CO 2 was unsatisfactory (erratic retention). Static restrictors (integral, frit, crimped Pt/Ir, linear, and valves) produced erratic flow. Heating the restrictors to 250–400 °C did not improve performance. Reasons for the compromise in chromatographic performance are proposed.

Lending industrial experience through reactive hazard examples in university safety instruction

Past serious reactive chemical accidents have had a profound impact on the chemical industry and the approaches taken toward process safety. Much of this knowledge has been picked up and presented as a part of the chemical engineering educational curriculum. However, the T2 Laboratories Inc., runaway reaction incident in 2007 provided the catalyst to spur AIChE and ABET to formally introduce a “process safety” education requirement into the accreditation program criteria. One of the areas that must become an integral part of the education of future chemical engineers is the understanding and recognition of reactive hazards. University professors have a key role in this education, and while some have had exposure to reactive hazards through industry experiences, it makes sense to invite industrial professionals to lend their expertise to the classroom. In this article, we describe a section on reactive hazards that has been developed and presented in the senior design classes in the Chemical and Biological Engineering Department at the South Dakota School of Mines and Technology. This section has been developed and presented jointly by university faculty and an engineer from industry. Hands‐on exercises and homework examples were developed to provide students with opportunities to apply important principles.

Technology enabled curriculum for a first-year engineering program

For the past three years, all first year engineering students at the South Dakota School of Mines & Technology have enrolled in a common introduction to engineering course. The course features a common curriculum contained on a course CD, utilization of technology tools, an engineering design project, and introduction to technical writing. All sections of the course are taught in a single classroom that is set up with tables and equipped with wireless notebook PCs. Technology tools are focused on collection, manipulation, and presentation of data using electronic portfolios, a permanent digital archive, spreadsheet tools, and data loggers. The use of spreadsheets for solving engineering problems is illustrated through example problems and several tutorial exercises that are both contained on the curricular CD. Portable data loggers are utilized in lab projects for collecting data that is then manipulated and analyzed on a spreadsheet. The design project requires students teams to function within specified design parameters, construct a simple device that is then used to collect data, analyze the data, and present the results both in an oral presentation and a formal technical document. In this paper, examples of technology uses in the curricular materials, engineering problems, and design projects used will be illustrated and discussed.