Chung-Sung Tan

Evaluation of alkanolamine solutions for carbon dioxide removal in cross-flow rotating packed beds.

The removal of CO(2) from a 10 vol% CO(2) gas by chemical absorption with 30 wt% alkanolamine solutions containing monoethanolamine (MEA), piperazine (PZ), and 2-amino-2-methyl-1-propanol (AMP) in the cross-flow rotating packed bed (RPB) was investigated. The CO(2) removal efficiency increased with rotor speed, liquid flow rate and inlet liquid temperature. However, the CO(2) removal efficiency decreased with gas flow rate. Also, the CO(2) removal efficiency was independent of inlet gas temperature. The 30 wt% alkanolamine solutions containing PZ with MEA were the appropriate absorbents compared with the single alkanolamine (MEA, AMP) and the mixed alkanolamine solutions containing AMP with MEA. A higher portion of PZ in alkanolamine solutions was more favorable to CO(2) removal. Owing to less contact time in the cross-flow RPB, alkanolamines having high reaction rates with CO(2) are suggested to be used. For the mixed alkanolamine solution containing 12 wt% PZ and 18 wt% MEA, the highest gas flow rate allowed to achieve the CO(2) removal efficiency more than 90% at a liquid flow rate of 0.54 L/min was of 29 L/min. The corresponding height of a transfer unit (HTU) was found to be less than 5.0 cm, lower than that in the conventional packed bed.

CO2 promoted hydrogenolysis of benzylic compounds in methanol and water

This study successfully demonstrated the hydrogenolysis of benzylic alcohols and their derivatives over a Pd/C catalyst by using CO2-expanded methanol (CX-methanol) and compressed CO2/water as two green reaction media. It was found that with the addition of low-pressure CO2 (1 MPa), the reaction conversions of benzylic alcohols and their derivatives could all be increased in the CO2 promoted systems. For example, the conversion of 1-phenylethanol could be elevated from 23% to 63% in CX-methanol and the conversion of benzyl alcohol could be elevated from 75% to 92% in compressed CO2/water. The positive effects of CO2 could be attributed to the decrease of mass transfer resistance and the increase of hydrogen solubility. CO2 could also form methylcarbonic acid and carbonic acid in methanol and water, respectively. Therefore, it could enhance the departing ability of the protonated hydroxyl leaving groups by providing a more acidic environment. In addition, the hydrogenolysis (or deoxygenation) of aromatic aldehyde and ketone by using compressed CO2/water as the solvent were also studied in this work. The results suggested that both CX-methanol and compressed CO2/water could be used as two efficient solvents for the hydrogenolysis reactions.

CO2 uptake performance and life cycle assessment of CaO-based sorbents prepared from waste oyster shells blended with PMMA nanosphere scaffolds

In this paper, we demonstrate a means of simultaneously solving two serious environmental issues by reutilization of calcinated mixture of pulverized waste oyster shells blending with poly(methyl methacrylate) (PMMA) nanospheres to prepare CaO-based sorbents for CO2 capture. After 10 cycles of isothermal carbonation/calcination at 750°C, the greatest CO2 uptake (0.19 g CO2/g sorbent) was that for the sorbent featuring 70 wt% of PMMA, which was almost three times higher than that (0.07 g CO2/g sorbent) of untreated waste oyster shell. The greater CO2 uptake was likely a result of particle size reduction and afterwards surface basicity enhancement and an increase in the volume of mesopores and macropores. Following simplified life cycle assessment, whose all input values were collected from our experimental results, suggested that a significant CO2 emission reduction along with lesser human health and ecosystems impacts would be achieved immediately once waste is reutilized. Most importantly, the CO2 uptake efficiency must be greater than 20% or sorbents prepared from limestone mining would eventually produce a net positive CO2 emission.

Catalytic hydrodechlorination of dioxins over palladium nanoparticles in supercritical CO2 swollen microcellular polymers

In this study, palladium nanoparticles embedded in monolithic microcellular high density polyethylene supports are synthesized as heterogeneous catalysts for remediation of 1,6-dichlorodibenzo-p-dioxin and 2,8-dichlorodibenzofuran in 200 atm of supercritical carbon dioxide containing 10 atm of hydrogen gas and at 50-90°C. Stepwise removal of chlorine atoms takes place first, followed by saturation of two benzene rings with slower reaction rates. The pseudo first order rate constant of initial hydrodechlorination for 2,8-dichlorodibenzofuran is 4.3 times greater than that for 1,6-dichlorodibenzo-p-dioxin at 78°C. The catalysts are easily separated from products and can be recyclable and reusable without complicated recovery and cleaning procedures.

Synthesis of phthalate-free plasticizers by hydrogenation in water using RhNi bimetallic catalyst on aluminated SBA-15

In this study, rhodium–nickel bimetallic nanoparticles loaded on aluminated silica (RhNi/Al-SBA-15) were used as catalysts for the hydrogenation of phthalate in water to produce environmentally acceptable non-phthalate plasticizers. Chemical fluid deposition (CFD) was used to dope metals onto the aluminated silica support, which helped to create a uniform structure of RhNi on Al-SBA-15. The introduction of Ni helped to reduce the use of expensive Rh and increase the number of metal active sites by reducing the bimetallic nanoparticle size. Aluminated SBA-15 not only acted as the support for the RhNi bimetallic catalyst but also enhanced the reaction efficiency by introducing Bronsted and Lewis acid sites and the absorption of phthalates on the catalyst in water. The physicochemical properties of prepared catalysts were characterized by N2 adsorption–desorption isotherm, X-ray diffraction (XRD), in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), Scanning electron microscopy (SEM), and Transmission electron microscopy (TEM). The catalytic performance of the synthesized catalysts was evaluated with the hydrogenation of dimethyl phthalate (DMP). Despite the low solubility of DMP in water, the hydrogenation using Rh0.5Ni1.5/Al-SBA-15 was carried out with an 84.4% reaction yield (cis-u2006:u2006trans- = 97.5u2006:u20062.5) at 80 °C using 1000 psi of H2 after 2 h.

Effect of distribution patterns of refractory overlayers on cyclic high temperature CO2 capture using waste oyster shell

Waste oyster shell powder has been applied in cyclic high temperature CO2 capture, but the sintering effect during calcium looping (carbonation/calcination) significantly shortens the life span of the adsorbents. The association of waste oyster shell with refractory materials, such as zirconium oxide has been evaluated, using either furnace treatment or atmospheric pressure plasma treatment to improve the thermal stability. It was noted that samples with 5 wt% of ZrO2, by either furnace treatment or plasma treatment, exhibited the highest CO2 capture capacity (∼360 mol-CO2 per mol-CaO in 20 calcium looping cycles). The plasma treatment was found to quite effectively enhance the thermal stability when more ZrO2 was added; however, evaporation–condensation reactions during plasma treatment led to evenly distributed CaZrO3 particles, which hindered the access of CO2 to CaO, and therefore reduced the overall CO2 capture capacity. In contrast, furnace treatment leads to most of the ZrO2 functioning as wedges to mitigate the sintering effect, which essentially exposes more CaO for CO2 access and accounts for its high overall CO2 capture capacity. Accordingly, the distribution patterns of refractory overlayers on waste oyster shell play an important role in cyclic high temperature CO2 capture.