Taesung Jung

Preparation of single-phase three-component alkaline earth oxide of (BaSrMg)O: a high capacity and thermally stable chemisorbent for oxygen separation

This study presents a preparation method for a single-phase three-component alkaline earth oxide of (BaSrMg)O that is a high capacity and thermally stable chemisorbent for oxygen separation based on the redox reaction cycle of BaO + 1/2O2 ↔ BaO2. First, single-phase (BaSr)CO3 is co-precipitated based on the reaction of Ba2+ and Sr2+ with CO32− in a solution, and then transformed to single-phase (BaSrMg)CO3 with the addition of an Mg2+ solution. When varying the reaction conditions, such as the reactant concentrations of Ba2+, Sr2+, Mg2+, and CO32− and the reaction temperature, (Ba0.52Sr0.06Mg0.42)CO3 crystals are identified as the most stable phase. The single-phase (BaSrMg)CO3 is then converted into single-phase (BaSrMg)O by thermal decomposition under an H2 atmosphere at 750 °C. According to a TGA analysis, the chemisorption and desorption of oxygen in (BaSrMg)O are very fast at t80 = 3.9 min and t80 = 14 min, respectively. In addition, the chemisorption capacity of (BaSrMg)O is higher at 2.02 mmol g−1 at 700 °C when compared with the chemisorption capacity of BaO/MgO at 1.75 mmol g−1 (Jin et al., Ind. Eng. Chem. Res., 2005, 44, 2942). (BaSrMg)O is also thermally stable due to the inclusion of Mg. Thus, the chemisorption capacity of (BaSrMg)O is unchanged, even over 10 redox reaction cycles. Additionally, the transient oxygen pressure required for the redox reaction of BaO–BaO2 is shifted from 76 mmHg to 148 mmHg due to the inclusion of Sr in (BaSrMg)O. Consequently, the three component alkaline earth oxide (BaSrMg)O can be a highly effective sorbent for industrial applications to oxygen separation in terms of the process design and operation.

Influence of polymeric additives on paraffin wax crystallization in model oils

Wax deposition, precipitation, and gelation make the transport of crude oil in pipelines challenging. The effect of several ethylene copolymers, and small molecules with a long alkyl chain, on wax formation was investigated for n-C32H66 in decane and de-aromatized white oil. Addition of a small amount of EVA (ethylene-co-vinyl acetate) copolymers delayed nucleation by reducing the onset temperature and the wax appearance temperature. They modified the wax crystal-structure and morphology from large plates to tiny particles by adsorbing to the wax surfaces and inhibiting growth. Viscosity and the pour-point were improved by inhibiting the formation of large aggregates. It was demonstrated that the content of vinyl acetate groups in EVA copolymers affected wax crystallization. The small molecules, propylene copolymers, and ethylene copolymers with ethyl acrylate, maleic anhydride, and ethylene glycol showed a weak inhibiting effect. The effect of wax inhibitors was determined by the content and by the type of structure-disturbing groups in the copolymers.

Preparation of Tunable (BaSrMg)O for Oxygen Chemisorption: Formation Mechanism and Characterization.

Composition-tunable single-phase three-component alkaline earth oxide of (BaSrMg)O was prepared based on the consecutive precipitation and thermal decomposition of (BaSrMg)CO3. First, the single-phase (BaSrMg)CO3 was coprecipitated via ion self-assembly, phase-transformation, and agglomeration. The element composition of (BaSrMg)CO3 could be simply tuned by the composition of the reactants. Then, (BaSrMg)CO3 was converted to (BaSrMg)O under an H2 atmosphere at 750 °C. This (BaSrMg)O showed fast chemisorption-desorption responses with oxygen chemisorption rate: t80 = 3.9 min and desorption rate: t80 = 14 min and a high thermal stability for the redox reaction of BaO-BaO2. In addition, the chemisorption capacity of (BaSrMg)O (4.39% Sr composition) is ∼1.92 mmol/g, which is much higher than the chemisorption capacity of BaO/MgO at 1.75 mmol/g (Jin et al., Ind. Eng. Chem. Res., 2005, 44, 2942), while the transient oxygen pressure for the redox reaction of (BaSrMg)O (4.39% Sr composition) was significantly enhanced from 76 to 135 mmHg due to the inclusion of Sr in (BaSrMg)O. The transient oxygen pressure could be further improved via adjusting the Sr composition in (BaSrMg)O. Consequently, the tunable (BaSrMg)O has a high potential as a chemisorbent for the industrial application of oxygen separation.

DYNAMIC BEHAVIOR OF PARTICLE AGGLOMERATION OF EUROPIUM OXALATE DURING REACTION CRYSTALLIZATION IN SEMI-BATCH REACTOR

ABSTRACT During reaction crystallization of europium oxalate in a semi-batch reactor, a monotonical increase in the mean particle size and corresponding reduction in the total particle population were observed due to particle agglomeration occurring simultaneously with particle nucleation and growth. However, since particle agglomeration was achieved via particle aggregation and molecular growth, the mean particle size and total particle population in the product suspension were significantly influenced by the crystallization conditions of the feed concentration, agitation speed, and feeding time. A higher feed concentration and feeding time resulted in a larger mean particle size and smaller total particle population due to the higher supersaturation and longer holding time in the reactor. Meanwhile, agitation was found to exhibit a rather complicated influence on particle agglomeration because particle collision and a turbulent fluid shear were both promoted at the same time. In the semi-batch reactor, the reduction in total particle population during crystallization clearly reflected particle agglomeration.