Boonyarach Kitiyanan

Synergism of Co and Mo in the catalytic production of single-wall carbon nanotubes by decomposition of CO

The catalyst composition and operating conditions for the synthesis of single-wall carbon nanotubes (SWNT) from CO decomposition have been systematically varied in order to maximize the selectivity towards SWNT. A simple quantification method based on the standard Temperature Programmed Oxidation (TPO) technique has allowed us to determine the distribution of the different forms of carbonaceous deposits present on the catalysts after the CO decomposition reaction. A synergistic effect between Co and Mo has been observed. When both metals are simultaneously present, particularly when Mo is in excess, the catalyst is very effective. However, when they are separated they are either inactive (Mo alone) or unselective (Co alone). To understand this synergistic effect, X-ray absorption spectroscopy (EXAFS and XANES) has been used to characterize the state of Co and Mo on the catalysts before and after the production of SWNT.

A Scalable Process for Production of Single-walled Carbon Nanotubes (SWNTs) by Catalytic Disproportionation of CO on a Solid Catalyst

Existing single-walled carbon nanotube synthesis methods are not easily scalable, operate under severe conditions, and involve high capital and operating costs. The current cost of SWNT is exceedingly high. A catalytic method of synthesis has been developed that has shown potential advantages over the existing methods. This method is based on a catalyst formulation that inhibits the formation of undesired forms of carbon; it can be scaled-up and may result in lower production costs.

Competitive Surfactant Adsorption of AOT and TWEEN 20 on Gold Measured Using a Quartz Crystal Microbalance with Dissipation

Competitive surfactant adsorption of anionic surfactant AOT and nonionic surfactant Tween 20 on gold was investigated by using a quartz crystal microbalance with dissipation (QCM-D) at 25 °C. The adsorption isotherm of pure AOT did not reach a plateau at the CMC, but rather adsorption continued to increase gradually at concentrations higher than the CMC before reaching a plateau. This behavior is evidence of competitive adsorption between AOT and impurities. The adsorbed layer of AOT on gold became more viscoelastic as the concentration of AOT increased. Tween 20 reached the plateau adsorption on gold before its concentration reached the CMC, suggesting that the attraction between Tween 20 and gold is very strong. The Tween 20 adsorbed layer was rigid when compared to the AOT adsorbed layer, as indicated by low dissipation. The addition of Tween 20 to a surface covered by AOT resulted in an increase in adsorbed mass, suggestive of the insertion of Tween 20 into the AOT adsorbed layer as expected because Tween 20 is able to separate the repulsive headgroups of AOT. When AOT was added to a preformed Tween 20 layer, a drop in the adsorbed amount was found between 0 and 0.1 CMC, and then no change was observed until the CMC of AOT was reached; the adsorbed amount then increased, reaching a final adsorption greater than that of pure AOT. All data support the formation of mixed surfactant layers on the surface. Although a two-step model fit both AOT and Tween 20 adsorption kinetic data well, AOT was found to adsorb much more slowly than Tween 20.

Separation of Carbon Black from Silica by Froth Flotation Part 1: Effect of Operational Parameters

Abstract Froth flotation can be applied to separate hydrophobic particles from hydrophilic ones in aqueous solution with the use of an appropriate surfactant. In this work, carbon black was separated from silica gel by means of froth flotation. Since the point of zero charge, or PZC, of the carbon black (3.5) is close to that of the silica gel (4.1), a nonionic surfactant (ethoxylated alcohol) was selected as the separating agent. Based on experimental results using a surfactant concentration of 62 µM or 75% of its critical micelle concentration (CMC), up to 70% of carbon black recovery was achieved with a carbon black enrichment ratio around 3.5. Added electrolyte (NaCl) showed a negligible effect on the separation efficiency. The presence of the surfactant was found to provide both a higher mass transfer surface area and to reduce the coalescence of air bubbles in the froth flotation column.

Synthesis of Well-Defined Oligo(2,5-dialkoxy-1,4-phenylene vinylene)s with Chiral End Groups: Unique Helical Aggregations Induced by the Chiral Chain Ends

Oligo(2,5-dialkoxy-1,4-phenylenevinylene)s containing three different chiral alkoxy substituents on the phenyl end groups with structurally regular (all trans) controlled repeat units have been prepared; these compounds showed highly enhanced aggregation-induced circular dichroism (AICD; formation of supramolecular polymers), and an inversion of the CD signal was observed even with the same end groups under certain conditions.

Purification of Single-Walled Carbon Nanotubes (SWNTs) by Acid Leaching, NaOH Dissolution, and Froth Flotation

The SWNTs with a carbon content of approximately 3% were synthesized via the disproportionation of CO over a CoMo/SiO2 catalyst. The three sequential steps, including acid treatment, silica dissolution, and froth flotation, were proposed for the purification of the as-synthesized SWNTs. The pretreatment step for the catalyst removal by acid leaching was optimized at an HCl concentration of 6 M, 50°C, and a sonication time of 3 h, corresponding to the Co and Mo removals of 84% and 44%, respectively. For the silica dissolution, the SWNTs sample after the acid leaching step was treated with a 5 M NaOH solution at 50°C and a sonication time of 3 h, leading to a silica removal of 54%. The froth flotation was employed to separate the SWNTs from the remaining silica using SDBS as an anionic frother. The process performance was maximized at an SDBS concentration of 0.1 × CMC, an air flow rate of 120 cm3/min, and a solution pH of 5, yielding a carbon content of the purified SWNTs of 71%. It was also found that the proposed technique successfully purified the as-synthesized SWNTs sample without damaging its nanostructure.

Effect of metal type and loading on hydrogen storage on NaAlH4

Although hydrogen has a great potential as clean energy, safe practical storage of hydrogen for applications such as fuel cells has been a major challenge. NaAlH4 is one of the metal hydrides, which are candidates for hydrogen storage in vehicles. However, the rather slow absorption/desorption kinetics is still a significant drawback. To alleviate this problem, purified NaAlH4 was ground with TiCl3, ZrCl4, or HfCl4. Desorption kinetics and capacities were observed under TPD-like operation. Absorption efficiency was determined by raising the temperature up to 125 8C. Of the three doped metals investigated for the positive effect on facilitating NaAlH4 decomposition, TiCl3 assists the best on the first reaction while ZrCl4 and HfCl4 do for the second one. Despite the kinetics enhancement directly involves with the ZrCl4 amount, there is a threshold of ZrCl4-content which affects. 6% ZrCl4 is considered as an appropriate amount to improve the hydrogen release because it simultaneously decreases the desorption temperature and gives the outstanding rate. In hydrogen desorption, ZrCl4 provides the most amount of released hydrogen, but for hydrogen absorption TiCl3-doped NaAlH4 possesses the highest capacity. It is believed that the metal size is one of the key factors resulting in such the behavior.

Effect of Catalyst Loading in Olefin Polymerization Catalyzed by Supported Half-Titanocenes on Polystyrene through Phenoxy Linkage

Half-titanocenes immobilized on the poly(styrene-co-hydroxystyrene) at various Ti loading have been prepared by the reaction with Cp*TiMe 3 . Effect of catalyst loading toward both the activity and the polymerization behavior was explored, and the catalysts at low Ti loading showed higher activity for ethylene polymerization. These catalysts also produced syndiotactic polystyrene with the moderate activity. However, the significant decrease in the activity was observed in the ethylene/1-hexene copolymerization, affording low molecular weight polymers.

Synthesis of methyl ester sulfonate surfactant from palm oil methyl ester by using UV or ozone as an initiator

Methyl ester sulphonate (MES) derived from palm oil is environmental friendly and offers good detergent properties. Although Alpha methyl ester sulphonate (α-MES) has been produced by many producers in detergent industries, it has some problems such as disalt formation and low water solubility. In order to overcome these drawbacks, MES is synthesized via sulphoxidation by using different initiators. Ozone is one of the most interesting agents because of its highly oxidizing power, which can react with organic compound rapidly under mild conditions. In this work, ozone and UV are used as an initiator in order to generate radicals along carbon chain to react with sulphur dioxide and oxygen. The reaction is performed in a photochemical reactor with UVC lamps (253.7 nm). The outlet product is transferred to separation and purification steps by liquid extraction techniques. The obtained products are analysed by FT-IR and ESIMS to confirm MES products. When reaction time is fixed at 4 h, conversions are around 7.5, 6.9 and 13.5 wt% for UV, ozone and UV/ozone systems, respectively.

Study of nonionic surfactants on HVOCs removal from coacervate solutions using cocurrent vacuum stripping in a packed column

ABSTRACT Cloud point extraction has been shown to be an effective technique to remove hydrophobic volatile organic compounds (HVOCs) from aqueous solution using nonionic surfactant. A cocurrent vacuum stripper is used to recover the surfactant in coacervate phase from extraction for economic viability. The solutions containing two series of aromatic and chlorinated HVOCs. Surfactants studied were alkyl phenol ethoxylates, secondary alcohol ethoxylates (AEs), and branched secondary AEs. From equilibrium measurements, the apparent Henry’s law constant (volatility) of the HVOCs in surfactant solution decreased with increasing HVOCs hydrophobicity due to solubilization of the HVOCs in micelles. The results showed that the mass transfer of HVOC decreases due to the solubilization enhancement of the HVOCs.