Hsunling Bai

Comparison of ammonia and monoethanolamine solvents to reduce CO2 greenhouse gas emissions

Abstract This paper presents experimental results on the evaluation of two reagents, ammonia (NH 3 ) and monoethanolamine (MEA) solvents, for scrubbing carbon dioxide (CO 2 ) greenhouse gas emissions. The scrubbing of CO 2 by NH 3 solvent is a novel study developed by the authors, and the MEA process is a traditional process for gas purification of removing CO 2 . The performance of these two solvents are compared in terms of CO 2 removal efficiency and absorption capacity. Test results show that both the CO 2 removal efficiency and absorption capacity of NH 3 solvent are better than those of MEA solvent under the operating conditions conducted in this study. The maximum CO 2 removal efficiency by NH 3 solvent can achieve 99% and the CO 2 absorption capacity can approach 1.20 kg CO 2 /kg NH 3 . On the other hand, the maximum CO 2 removal efficiency and absorption capacity by MEA solvent are 94% and 0.40 kg CO 2 /kg MEA, respectively, under the same operating conditions tested by NH 3 solvent. Besides, the temperature increases due to exothermal reactions in the NH 3 scrubbing process are lower than those in the MEA scrubbing process. This indicates that the energy requirement for the regeneration of NH 3 reagent should be less than that for the regeneration of MEA reagent.

Capture of CO2 from flue gas via multiwalled carbon nanotubes

Carbon nanotubes (CNTs) were modified by 3-aminopropyl-triethoxysilane (APTS) solution and were tested for its CO2 adsorption potential at multiple temperatures (20-100 degrees C). The physicochemical properties of CNTs were changed after the modification, which makes CNTs adsorb more CO2 gases. The adsorption capacities of CO2 via CNTs and CNTs(APTS) decreased with temperature indicating the exothermic nature of adsorption process and increased with water content in air at 0-7%. The mechanism of CO2 adsorption on CNTs and CNTs(APTS) appears mainly attributable to physical force regardless of temperature change, which makes regeneration of spent CNTs at a relatively low temperature become feasible. The CNTs(APTS) have good adsorption performance of CO2 at 20 degrees C as compared to many types of modified carbon or silica adsorbents documented in the literature. This suggests that the CNTs(APTS) are promising low-temperature adsorbents for CO2 capture from flue gas.

AN EXPERIMENTAL STUDY ON THE PERFORMANCE OF A SINGLE DISCHARGE WIRE-PLATE ELECTROSTATIC PRECIPITATOR WITH BACK CORONA

The phenomenon of back corona is well known in that it may reduce the collection efficiency of an electrostatic precipitator. In this study, experimental results are presented for the influence of back corona on the performance of a laboratory scale single-discharge-wire ESP system. The effect of back corona under two power controlled methods, constant voltage operation and constant current operation, has been evaluated. The experimental results showed that as back corona occurs, the output current and the power consumption are increased under constant voltage operation. The mass collection efficiency is proportional to the applied voltage. On the other hand, for constant current operation the voltage and the power consumption are decreased under back corona. The mass collection efficiency is independent of the applied current. A lateral mixing model was also applied to assist in the discussion of corona power and particle collection efficiency under normal and stable back corona conditions. Both experimental and theoretical results indicated that the back corona has a large effect on submicron particles. The grade efficiency can be reduced by over 60% for submicron particles. The large reduction of efficiency for submicron particles is due to significant reduction in both particle charge and migration velocity. Since particles in the submicron region are more sensitive to light scattering, the opacity problem may be aggravated under back corona.

Organic Airborne Molecular Contamination in Semiconductor Fabrication Clean Rooms A Review

Monitoring of airborne molecular contamination (AMC) has become a crucial element of cleanroom management as the production phase of semiconductor devices marches deep into sub-100-nm range. The current understandings of the AMC, particularly those with organic origins, are presented comprehensively in this article based on the research reports within the past ten years. Starting with a review of the chronological development of AMC problems and several approaches for the AMC classifications, this article also examines the merits of several available ambient sampling and surface analytical methods. The focal point of the article is to address the surface deposition potential of organic AMCs by experimentally correlating the surface speciation and abundance of the organic AMCs with their physical and chemical characteristics, together with the kinetic models delineating the rates of deposition for both single-and multiple-contaminant scenarios. In addition, the current progress of the AMC control strategies, especially the development of the chemical filtration technology, is also examined in the paper.

Bromocresol Green/Mesoporous Silica Adsorbent for Ammonia Gas Sensing via an Optical Sensing Instrument

A meso-structured Al-MCM-41 material was impregnated with bromocresol green (BG) dye and then incorporated into a UV-Vis DRA spectroscopic instrument for the online detection of ammonia gas. The absorption response of the Al-MCM-41/BG ammonia sensing material was very sensitive at the optical absorption wavelength of 630 nm. A high linear correlation was achieved for ppmv and sub-ppmv levels of ammonia gas. The response time for the quantitative detection of ammonia gas concentrations ranging from 0.25 to 2.0 ppmv was only a few minutes. The lower detection limit achieved was 0.185 ppmv. The color change process was fully reversible during tens of cycling tests. These features together make this mesoporous Al-MCM-41 material very promising for optical sensing applications.

Continuous generation of TiO2 nanoparticles by an atmospheric pressure plasma-enhanced process

A novel method for the continuous generation of titanium dioxide (TiO2) nanoparticles by dielectric barrier discharge process is presented using titanium tetraisopropoxide (TTIP) and water as precursors. The aerosol generator employs an atmospheric pressure plasma enhanced nanoparticle synthesis (APPENS) process of alternative current (AC). The influences of applied voltage, frequency and precursor molar ratio on the generated particles were described by the SEM, XRD, and SMPS analyses. The results showed that TiO2 particles appear to be in a broad size range of bi-modal distribution when no voltage is applied. While after applying the AC plasma they become uni-modal distributed with average sizes range from around 30 to 60 nm. The applied electric frequency can be adjusted to either generate nanoparticles after the plasma reactor or develop a thin film in the reactor. An increase in the precursor molar ratio leads larger particles with a broader size distribution.

Adsorption and Desorption Characteristics of Semiconductor Volatile Organic Compounds on the Thermal Swing Honeycomb Zeolite Concentrator

Abstract The use of a honeycomb zeolite concentrator and an oxidation process is one of the most popular methods demonstrated to control volatile organic compound (VOCs) emissions from waste gases in semiconductor manufacturing plants. This study attempts to characterize the performance of a concentrator in terms of the removal efficiencies of semiconductor VOCs (isopropyl alcohol [IPA], acetone, propylene glycol methyl ether [PGME], and propylene glycol monomethyl ether acetate [PGMEA]) under several parameters that govern the actual operations. Experimental results indicated that at inlet temperatures of under 40 °C and a relative humidity of under 80%, the removal efficiency of a zeolite concentrator can be maintained well over 90%. The optimal rotation speed of the concentrator is between 3 and 4.5 rph in this study. The optimal rotation speed increases with the VOCs inlet concentration. Furthermore, reducing the concentration ratio helps to increase the removal efficiency, but it also increases the incineration cost. With reference to competitive adsorption, PGMEA and PGME are more easily adsorbed on a zeolite concentrator than are IPA and acetone because of their high boiling points and molecular weights.

Biotreatment of hydrogen sulfide- and ammonia-containing waste gases by fluidized bed bioreactor.

ABSTRACT Gas mixtures of H2S and NH3 are the focus of this study of research concerning gases generated from animal husbandry and treatments of anaerobic wastewater lagoons. A heterotrophic microflora (a mixture of Pseudomonas putida for H2S and Arthrobacter oxydans for NH3) was immobilized with Ca-alginate and packed into a fluidized bed reactor to simultaneously decompose H2S and NH3. This bioreactor was continuously supplied with H2S and NH3 separately or together at various ratios. The removal efficiency, removal rate, and metabolic product of the bioreactor were studied. The results showed that the efficiency remained above 95% when the inlet H2S concentration was below 30 ppm at 36 L/hr. Furthermore, the apparent maximum removal and the apparent half-saturation constant were 7.0 x 10-8 g-S/cell/day and 76.2 ppm, respectively, in this study. The element sulfur as a main product prevented acidification of the biofilter, which maintained the stability of the operation. As for NH3, the greater than 90% removal rate was achieved as long as the inlet concentration was controlled below 100 ppm at a flow rate of 27 L/hr. In the NH3 inlet, the apparent maximum removal and the apparent half-saturation constant were 1.88 x 10-6 g-N/cell/day and 30.5 ppm, respectively. Kinetic analysis showed that 60 ppm of NH3 significantly suppressed the H2S removal by Pseudomonas putida, but H2S in the range of 5-60 ppm did not affect NH3 removal by Arthrobacter oxydans. Results from bioaerosol analysis in the bioreactor suggest that the co-immobilized cell technique applied for gas removal creates less environmental impact.

Photocatalytic removal of NO and NO2 using titania nanotubes synthesized by hydrothermal method

In this study, the photocatalysts of titania nanotubes (TNTs) were synthesized at different calcination temperatures using commercial Degussa TiO2 (P25) as a precursor. The materials were then characterized by BET, SEM, TEM, and XRD analyses. The photocatalytic reactions with NO and NO2 under UV-A irradiation were both performed. The results showed that the photocatalytic reaction rate of NO was much faster than that of NO2, and the conversion of NO2 to nitrate was the rate-limiting step for photocatalytic removal of NOx if the nitrate produced cannot be removed continuously from the photocatalyst surface. For TNTs calcined at different temperatures, a significant enhancement was observed on the total NOx removal efficiency by TNT calcined at 500°C for both NO and NO2 photocatalytic reaction, which could be attributed to its high anatase crystallinity as well as high surface area. These two factors affect primarily on the NO2 conversion step in which the high anatase crystallinity could be responsible for the high efficiency at the beginning, while the high surface area could be accounted for retaining this high efficiency from nitric acid poisoning during the test period.

Silica materials recovered from photonic industrial waste powder: Its extraction, modification, characterization and application

This study explored the possibility of recovering waste powder from photonic industry into two useful resources, sodium fluoride (NaF) and the silica precursor solution. An alkali fusion process was utilized to effectively separate silicate supernatant and the sediment. The obtained sediment contains purified NaF (>90%), which provides further reuse possibility since NaF is widely applied in chemical industry. The supernatant is a valuable silicate source for synthesizing mesoporous silica material such as MCM-41. The MCM-41 produced from the photonic waste powder (PWP), namely MCM-41(PWP), possessed high specific surface areas (1082 m(2)/g), narrow pore size distributions (2.95 nm) and large pore volumes (0.99 cm(3)/g). The amine-modified MCM-41(PWP) was further applied as an adsorbent for the capture of CO(2) greenhouse gas. Breakthrough experiments demonstrated that the tetraethylenepentamine (TEPA) functionalized MCM-41(PWP) exhibited an adsorption capacity (82 mg CO(2)/g adsorbent) of only slightly less than that of the TEPA/MCM-41 manufactured from pure chemical (97 mg CO(2)/g adsorbent), and its capacity is higher than that of TEPA/ZSM-5 zeolite (43 mg CO(2)/g adsorbent). The results revealed both the high potential of resource recovery from the photonic solid waste and the cost-effective application of waste-derived mesoporous adsorbent for environmental protection.