Chintana Saiwan

The development of gas sensor for carbon monoxide monitoring using nanostructure of Nb–TiO2

Abstract The development of titanium dioxide (TiO2) as a gas sensor for combustion and exhaust air pollutants monitoring is strongly dependent on its properties such as thermal stability, grain size and surface area. In this study, nanostructure TiO2 with its thermal stability enhanced by niobium dopant (Nb–TiO2) was synthesized using the water-in-oil (w/o) microemulsion system of n-heptane/water/sodium bis (2-ethylhexyl) sulfosuccinate (AOT) surfactant and was compared with undoped TiO2. It was found that the synthesized powder was of uniform size (14 nm) and high surface area (80 m2/g). Nb-doped TiO2 at a level of 3–5 mole% clearlyhinders the anatase to rutile phase transformation and inhibits the grain growth in comparison with pure TiO2. The nanostructure of anatase was maintained even after the powder was fired at 850 °C. The result indicates that sensitivity of CO is significantly increased with an increase of thermal stability of Nb-doped TiO2 in comparison with those of undoped TiO2 and thus is useful for CO sensing studies at high temperatures.

Use of Poly electrolyte-Enhanced Ultra filtration to Remove Chromate from Water

Abstract Poly electrolyte-enhanced ultra filtration (PEUF) is a process which can be used to remove multivalent ions from water. In PEUF a poly electrolyte of opposite charge to the target ion is added to the water to bind the ion to be removed. The solution is then treated using ultra filtration with membrane pore sizes small enough to reject the polymer and bound ion. In this study, chromate (CrO2 4 −) is removed from water using poly(diallyldimethyl ammonium chloride) with an average molecular weight of 240K as the poly electrolyte. In the absence of other added electrolytes, chromate rejections of up to 99.8% were observed. The presence of added NaCl reduces the chromate rejection substantially. A study of the flux of the system yielded a gel concentration of 0.55 M cationic poly electrolyte. This high gel concentration and high rejection mean that the ultra filtration can produce a concentrated, low-volume waste stream, and a purified stream containing chromate at low concentration.

Polyelectrolyte-enhanced ultrafiltration of chromate, sulfate, and nitrate

Polyelectrolyte-enhanced ultrafiltration (PEUF) involves addition of a polyelectrolyte of opposite charge to that of the multivalent ions to be removed from the contaminated water. In this study, a water-soluble polyelectrolyte, poly(diallyldimethyl ammonium chloride) or QUAT is added to the aqueous solutions containing divalent anions chromate or sulfate. Removal of monovalent anion nitrate is also studied to probe the effect of valence. The water is then passed through an ultrafiltration membrane with pore size small enough to reject the polyelectrolyte with the bound target ions. The rejection of anions increases with increasing concentration ratio of QUAT to anion. A high QUAT concentration in the retentate decreases relative flux due to accumulation of polyelectrolyte near the membrane surface (hydrodynamic boundary layer). Rejections of chromate and sulfate are similar and >98% at reasonable operating conditions. Rejection of nitrate is substantially below that of the divalent anions, but can be as high as 97% under feasible operating conditions. The gel concentration (where flux approaches zero) of the QUAT varied from 5.1 to 8.1 wt%.

Use of foam flotation to remove tert-butylphenol from water

The surfactants cetyl pyridinium chloride (CPC) and sodium dodecyl sulfate (SDS) were used in a study of an adsorptive bubble flotation process in batch mode to remove tert-butylphenol (TBP) from water. The TBP removal is maximized when the surfactant concentration is around the critical micelle concentration (CMC). Since micelles form above the CMC, this indicate that the higher the surfactant monomer concentration, the better the removal, but the micelles compete with the air/water interface for the TBP, resulting in micelles reducing removal efficiency. The addition of NaCl to the feed solution results in a significant reduction of the ability of CPC to remove TBP, while it improves the ability of SDS to remove TBP.

Part 3: Corrosion and prevention in post-combustion CO2 capture systems

This article is part 3 of the review series on ‘Recent progress and new development of post-combustion carbon capture technology using reactive solvents’. This review focuses on alkanolamine absorption during post-combustion CO2 capture from coal-fired flue gas, looking at a range of absorbents, including those that are commonly used, as well as blended and new solvents. The effects on corrosion of blended and new absorbents and process parameters (e.g., amine concentration, CO2 loading, oxygen concentration, SO2 concentration and temperature) are reviewed. Also reviewed is the effect of corrosion on the formation of heat-stable salts in the absorbent stream, as well as the presence of impurities in flue gas. Finally, corrosion mechanisms are discussed and corrosion inhibition approaches are reviewed.

Densities and low pressure solubilities of carbon dioxide in five promising ionic liquids

Ionic liquids are presently considered the most energy-efficient and environmentally benign solvents for CO2 capture. This research aimed at measuring the solubility of CO2 in five room temperature ionic liquids, triethylsulfoniumbis(trifluoromethylsulfonyl)imide ([S222][Tf2N]), diethylmethyl(2-methoxy ethyl)-ammonium bis(trifluoromethylsulfonyl)imide ([deme][Tf2N]), 1-propyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([pmim][Tf2N]), 1-allyl-3-methylimidazolium bis-(trifluoromethyl sulfonyl)imide ([amim][Tf2N]), and 1-butyl-4-methylpyridinium tetrafluoroborate ([4mbp][BF4]) at (313.15, 323.15 and 333.15 K) and at pressures up to 20 bar using a gravimetric microbalance. The experimental solubility data of CO2 in these solvents were well correlated using the Peng–Robinson (PR-EoS), Redlich–Kwong–Soave (SRK-EoS), SRK-EoS with quadratic mixing rules, and the Non-Random Two-Liquid (NRTL) with satisfactory average absolute deviations (AADs). Binary interaction parameters for these correlations were also reported. The absorption of CO2 was prone to diminish in this sequence: [deme][Tf2N] > [pmim][Tf2N] > [amim][Tf2N] > [S222][Tf2N] > [4mbp][BF4]. The four ionic liquids {[deme][Tf2N], [pmim][Tf2N], [amim][Tf2N], and [S222][Tf2N]} are deemed promising due to comparably high CO2 absorption (physical) to other prevalent CO2-absorbing ionic liquids. More interestingly, [deme][Tf2N] is shown to have the highest CO2 solubility among all ammonium-based ionic liquids reported in the literature. In addition, Henrys law constants, enthalpies and entropies of absorption for CO2 in the investigated ionic liquids were also reported.

Part 6: Solvent recycling and reclaiming issues

Purification of solvents is required to maintain quality and absorption capacity for better performance and economics for CO2 capture plants. An effective technique is needed to separate degradation products from their parent amines to prevent operational problems such as corrosion, foaming, fouling and change of solvent physicochemical properties. To overcome these problems, an amine reclamation process is used to clean up the solvent. Over 30 years ago, only five amine clean-up methods – solvent changeover, solvent purging/feeding, mechanical filtration, activated carbon filtration and neutralization of organic/inorganic acids – existed, which are reviewed in this article. More specific and advanced approaches developed later to achieve more effective removal of impurities and degradation products from the solvents are also summarized. This article also gives future trends for reclamation techniques in amine-based CO2 capture processes including hybrid processes or improvement of the current technologies such as extraction, ion exchange, thermal distillation and electrodialysis.

The Roles of O2 and SO2 in the Degradation of Monoethanolamine during CO2 Absorption from Industrial Flue Gas Streams

The roles of O₂ and SO₂ in the degradation of aqueous monoethanolamine (MEA) in the concentration range of 5 - 7 kmol/m³ were investigated using simulated flue gas containing O₂ of 6- 100 %, and SO₂ concentration in the range of 10^-11 -11 ppm, as typically present in polished flue gas streams, at degradation temperatures in the range of 328 - 393 K. An analysis of a power law rate expression formulated to represent the degradation process showed that the degradation was most susceptible to O₂ followed by MEA and then SO₂. SO₂ played a significant role by giving rise to additional MEA oxidative degradation. An increase in O₂ and SO₂ concentrations, the initial MEA concentration, and temperature all resulted in an increase of the degradation rate.

Ecological dyeing of silk fabric with lac dye by using padding techniques

This research focuses on silk fabrics exhibiting different colour values and fastness properties. The samples were prepared by dyeing with lac as a natural colourant. Two padding techniques were used in the process, namely, the pad-batch and pad-dry techniques, under different conditions. Aluminium potassium sulphate, ferrous sulphate, copper sulphate and stannous chloride were used as mordants. The effects of differing dye concentrations added to the silk fabrics using a pre- and post-mordant method were studied and recorded. The colour fastness to washing, light, rubbing, water and perspiration of the dyed samples was performed according to the present ISO standard. Silk fabric dyed without mordant showed a pink shade, while those samples mordanted with stannous chloride and aluminium potassium sulphate displayed noticeably brighter red coloured shades. With the additional use of copper sulphate, the colour shade produced was violet, while darker grey shades were obtained by adding ferrous sulphate mordant. The test results regarding fastness properties ranged from fair to very good, while wash fastness ranged from very poor to poor.

Eco-Dyeing of Silk Fabric with Garcinia Dulcis (Roxb.) Kurz Bark as a Source of Natural Dye by using The Padding Technique

Silk fabrics were put through a process of dyeing with natural colorants extracted and used from the bark of the Garcinia dulcis (Roxb.) Kurz. Two padding techniques, pad-batch and pad-dry, were used under different study conditions. The effects of mordant agents used on the fabrics and the natural colorant in the dyeing process, color values, color strength, and the fastness properties of silk fabric were investigated and the results recorded in the following study. The results showed that color values can be changed using various metallic salts as mordants. The fastness properties ranged from fair to very good, while perspiration and light fastness was poor to fair.