Youn-Woo Lee

Preparation of L-PLA Submicron Particles by a Continuous Supercritical Antisolvent Precipitation Process

Submicron particles of L-polylactic acid (L-PLA) without residual solvent were prepared by a continuous supercritical antisolvent (SAS) recrystallization process. Methylene chloride (CH2C12) was used as a carrier solvent of L-PLA. Experiments were performed with changing process parameters such as pressure and temperature at constant concentration. Also, L-PLA initial concentrations in methylene chloride were varied from 0.3 to 4 wt%. The flow rates of CO2 and solution, which were introduced into the precipitator, and nozzle diameter were kept unchanged in all of the experiments. It was found that the SAS process gives fine tuning of particle size and particle size distribution (PSD) by simple manipulations of the process parameters. In all cases of SAS recrystallization experiments, the formed spherical fine particles with a smooth surface were non-agglomerated and free flowing. Mean particle size of the L-PLA microparticles formed was varied from 0.1 to 1 μm by means of adjusting the system pressure and/or temperature.

Phase equilibria of CFC alternative refrigerant mixtures : 1,1,1,2,3,3,3-Heptafluoropropane (HFC-227ea) + difluoromethane (HFC-32), + 1,1,1,2-tetrafluoroethane (HFC-134a), and + 1, 1-difluoroethane (HFC-152a)

Isothermal vapor–liquid equilibria were measured for the binary systems difluoromethane (HFC-32)+1,1,1,2,3,3,3-heptafluoropropane (HFC-22ea) and 1,1-difluoroethane (HFC-152a)+1,1,1,2,3,3,3-heptafluoropropane at 283.15 and 303.15 K and 1,1,1,2-tetrafluoroethane (HFC-134a)+1,1,1,2,3,3,3-heptafluoropropane at 303.15 and 323.15 K in an apparatus in which both phases were recirculated. The experimental data were correlated with the Peng–Robinson equation of state using the Wong–Sandler mixing rules. Azeotropic behavior has not been found in any of the three mixtures.

Mass-transfer and hydraulic characteristics in spray and packed extraction columns for supercritical carbon dioxide-ethanol-water system

Abstract Mass-transfer efficiencies and hydraulic characteristics of a 3.18-cm spray and a packed column for extracting ethanol from aqueous ethanol solution with supercritical carbon dioxide were investigated. Experiments were performed at 308.2, 313.2, and 323.2 K over a pressure range from 9.1 to 12.2 MPa. The influences of fluid properties, phase flow rates, column internals, and phase dispersion on mass-transfer efficiencies and hydraulic characteristics are discussed. An extension of a model for predicting mass-transfer efficiency in conventional liquid-liquid extraction to supercritical-fluid extraction was attempted. The model for mass-transfer efficiencies, developed for conventional spray and packed liquid-liquid extraction columns, was in good agreement with our experimental results.

Uncatalyzed partial oxidation of p-xylene in sub- and supercritical water

In sub- and supercritical water, partial oxidation of p-xylene was performed in a batch reactor without a catalyst at 240-500oC, 220-300 bar. The loaded amount of hydrogen peroxide was set to 0-100% of the theoretically required oxygen amount. Conversion of p-xylene was reached over 99% within 15-20 min. In sub- and supercritical water, we propose two parallel pathways and major products that consist of p-tolualdehyde, p-toluic acid, terephthalic acid, toluene and benzaldehyde. Yields of major products in subcritical conditions were higher than in a supercritical conditions.

Total organic carbon disappearance kinetics for supercritical water oxidation of dimethyl methylphospate used as a chemical agent simulant

Supercritical Water Oxidation (SCWO) has been proven to be a powerful technology to treat a wide range of wastes, but there are few references in the literature about the application of SCWO to chemical weapon agents. In this work, SCWO has been tested to treat a chemical agent stimulant, dimethyl methylphosphonate (DMMP), which is similar to the nerve agent VX and GB (Sarin) in its structure. The experiments were performed in an isothermal tubular reactor with H2O2 as an oxidant. The reaction temperatures ranged from 398 to 633 ‡C at a fixed pressure of 24 MPa. The conversion of DMMP was monitored by analyzing total organic carbon (TOC) on the liquid effluent samples. It was found that the oxidative decomposition of DMMP proceeded rapidly and a high TOC decomposition up to 99.99% was obtained within 11 seconds at 555 ‡C. An assumed first-order global power-law rate expression was determined with activation energy of 32.35±2.21 kJ/mol and a pre-exponential factor of 54.63±1.45 s ’ to a 95% confidence level. By taking into account the dependence of the reaction rate on oxidant concentration, a global power-law rate expression was regressed from the complete set of data. The resulting activation energy was 42.00±0.41 kJ/ mol; the pre-exponential factor was 66.56±0.48l1.31 mmol-0.31 s-1; and the reaction orders for DMMP (based on TOC) and oxidant were 0.96±0.02 and 0.35±0.04, respectively.

Supercritical Carbon Dioxide debinding in metal injection molding (MIM) process

The conventional debinding process in metal injection molding (MIM) is critical, environmentally unfriendly and time consuming. On the other hand, supercritical debinding is thought to be an effective method appropriate for eliminating the aforementioned inconvenience in the prior art. In this paper, supercritical debinding is compared with the conventional wicking debinding process. The binder removal rates in supercritical CO2 have been measured at 333.15 K, 348.15 K, and 358.15 K in the pressure range from 20 MPa to 28 MPa. After sintering, the surface of the silver bodies were observed by using SEM. When the supercritical CO2 debinding was carried out at 348.15 K, all the paraffin wax (71 wt% of binder mixture) was removed in 2 hours under 28 MPa and in 2.5 hours under 25 MPa. We also studied the cosolvent effects on the binder removal rate in the supercritical CO2 debinding. It was found that the addition of non-polar cosolvent (n-hexane) dramatically improves the binder removal rate (more than 2 times) for the paraffin wax-based binder system.

PREPARATION OF ULTRA-PURE SUCCINONITRILE BY COUNTERCURRENT DISTILLATION FOR CRYSTAL GROWTH

We developed the purification method to produce ultra-pure succinonitrile by multiple countercurrent distillations. The distillation column used was 25 mm in diameter and 110 cm in the packed height with Heli-Pak® packing (0·05” × 0·10” × 0·10”, packing factor+ 960). Typical operational conditions of each stage are as follows: condenser temperature 65 °C, reboiler temperature 160 °C, head pressure 50 m Torr or below, and reflux ratio of 60:1. As the number of distillation stages increases, the maximum temperature of the freezing curve increases and the freezing curves become flat. Triple point of our sample, which is obtained after eight distillation stages, is not appreciably different from that of a standard NIST specimen. The purity of the SCN prepared in our experiments is estimated at 99·99992% which corresponds to a melting range (T1, – Ts) of 1·2 mK. To ensure the purity of our purified SCN for the purpose of crystal growth, the growth rate and the tip radius of dendrite were measured at various su...