Akihiro Yamasaki

A new CO2 disposal process via artificial weathering of calcium silicate accelerated by acetic acid

A new disposal process for anthropogenic CO2 via an artificially accelerated weathering reaction is proposed to counteract global warming. The process is essentially composed of the following two steps:(1)CaSiO3+2CH3COOH→Ca2++2CH3COO−+H2O+SiO2(2)Ca2++2CH3COO−+CO2+H2O→CaCO3↓+2CH3COOHStep (1) is the extraction of calcium ions by acetic acid from calcium silicate, for example, wollastonite rocks. Step (2) is the deposition of calcium carbonate from the solution of calcium ions by CO2 injection. The Gibbs free energy change of each step is negative; the reactions would proceed spontaneously without consuming large amounts of energy. The CO2 would be captured from the concentrated emission sources such as thermal power plant, and be disposed of and sequestrated in the form of calcium carbonate. The feasibility of the proposed process was evaluated through a process design based on the experimental results of the reaction kinetics. The operational energy consumption was 20.4 MW for the disposal of CO2 produced by a 100-MW thermal power plant.

PERVAPORATION OF ETHANOL/WATER THROUGH A POLY (VINYL ALCOHOL)/CYCLODEXTRIN(PVA/CD) MEMBRANE

Abstract A poly(vinyl alcohol)/cyclodextrin (PVA/CD) membrane was utilized in the pervaporation of ethanol/water mixtures. The membrane was prepared by casting an aqueous solution of PVA and β-cyclodextrin oligomer. The CD oligomer was successfully immobilized in the membrane by the crosslinking of PVA with glutaraldehyde for 1 h. The content of CD was up to 33%. The effect of CD on the pervaporation performances of water/ethanol was investigated by measurements of the sorption equilibrium and the calculations of the diffusion coefficient of the permeants in the membrane. The addition of CD increased the water selectivity of the pervaporation of water/ethanol, especially at lower (

Pervaporation of benzene/cyclohexane and benzene/n-hexane mixtures through PVA membranes

Poly(vinyl alcohol) (PVA) membranes (both homogeneous and asymmetric) were studied for the pervaporation separation of benzene/n-hexane and benzene/cyclohexane mixtures. The asymmetric PVA membrane with skin and porous layers was prepared through the phase inversion technique. Both asymmetric and homogeneous membranes were benzene-selective for all the feed compositions. The benzene separation factor of homogeneous PVA membrane was smaller than three, and the total permeation flux was several g/m2/h. The benzene selectivity of the asymmetric PVA membrane was much higher than that of the homogeneous membrane; weight fraction of benzene in the permeate side was larger than 90% for all the feed compositions. On the other hand, the total flux was almost unchanged compared with that of the homogeneous membrane. These results indicate that the density of the skin layer of the asymmetric membrane should be much higher than that of the homogeneous membrane.

Preparation and performance of arsenate (V) adsorbents derived from concrete wastes

Solid adsorbent materials, prepared from waste cement powder and concrete sludge were assessed for removal of arsenic in the form of arsenic (As(V)) from water. All the materials exhibited arsenic removal capacity when added to distilled water containing 10-700 mg/L arsenic. The arsenic removal isotherms were expressed by the Langmuir type equations, and the highest removal capacity was observed for the adsorbent prepared from concrete sludge with heat treatment at 105°C, the maximum removal capacity being 175 mg-As(V)/g. Based on changes in arsenic and calcium ion concentrations, and solution pH, the removal mechanism for arsenic was considered to involve the precipitation of calcium arsenate, Ca3(AsO4)2. The enhanced removal of arsenic for the adsorbent prepared from concrete sludge with heat treatment was thought to reflect ion exchange by ettringite. The prepared adsorbents, derived from waste cement and concrete using simple procedures, may offer a cost effective approach for arsenic removal and clean-up of contaminated waters, especially in developing countries.

Field validation of an active sampling cartridge as a passive sampler for long-term carbonyl monitoring

Abstract A carbonyl sampler originally designed for the active sampling method (Sep-Pak XPoSure) was used for long-term passive sampling, and its applicability as a passive sampler was examined through field experiments. The uptake rates of passive sampling were determined experimentally from collocated passive and active samplings for various sampling periods. The obtained uptake rates of formaldehyde, acetaldehyde, and acetone were 1.48, 1.23, and 1.08 mL/min, respectively. These uptake rates were consistent for a wide range of the sampling term (12 hr–2 weeks). Uptake rates of each carbonyl were proportional to the diffusion coefficients of each. Therefore, the ratios of diffusion coefficients were used to calculate the uptake rates of carbonyls for which the rates were not determined experimentally. Lower limits of determination were 2.16–17.5 μg/m3 for 2-week sampling. It was confirmed that 2-week monitoring of carbonyl concentrations up to 118–229 μg/m3 was possible. Relative standard deviations of the passive method generated from the repeatability test were 2–12.3% error for five samplings, and the recovery efficiencies were larger than 90%. Thus, the passive sampler was found to be highly suitable for long-term monitoring of carbonyl compounds.

Pressure-mole fraction phase diagrams for co 2 -pure water system under temperatures and pressures corresponding to ocean waters at depth to 3000 M

Pressure-mole fraction phase diagrams for the CO 2 -water system at temperatures between 278.15 and 298.15 K and pressures up to 30 MPa, which correspond to those of ocean waters at depths to 3000 m, are developed based on the literature data and experimental results obtained by the authors. The resultant phase diagrams can serve as a basis for analyzing the phase behavior of liquid CO 2 and CO 2 hydrate disposed of in the ocean as a means to mitigate global warming.

A CO2 fixation process with waste cement powder via regeneration of alkali and acid by electrodialysis

A mineral carbonation process for CO2 sequestration has been developed, and its process feasibility was examined based on laboratory-scale experimental studies. The process is composed of four steps: (i) extraction of calcium ions from waste cement powder with nitric acid. (ii) Absorption of CO2 in sodium hydroxide solution from CO2 emission sources. (iii) Precipitation of calcium carbonate particles by mixing the calcium leached solution and the CO2 absorbed solution. (iv) Regeneration of nitric acid and sodium hydroxide from the remaining solution of sodium nitrate from step (iii) with bipolar membrane electrodialysis. The regenerated acid and alkali can be reused in steps (i) and (ii) with newly fed waste cement powder. The overall mass balance of the process is the input of CO2 and calcium and the output of calcium carbonate and residues of the leaching. The effects of the operation conditions in the calcium leaching step (i) and regeneration step (iv) were experimentally investigated with a laboratory-scale experimental apparatus. It was found that calcium leaching can be easily and quickly performed with nitric acid, and high-purity calcium carbonate can be obtained when the operation conditions are set to obtain a final pH of about 7. Regeneration of nitric acid and sodium hydroxide were favourable when the current density and the electric potential were high and the feed concentration was low in terms of the power consumption. Thus, the total process can be operated under appropriate conditions, and its CO2 fixation performance was evaluated.

Development of a Combined Real Time Monitoring and Integration Analysis System for Volatile Organic Compounds (VOCs)

A combined integration analysis and real time monitoring (Peak Capture System) system was developed for volatile organic compounds (VOCs). Individual integration analysis and real time monitoring can be used to qualitatively and quantitatively analyze VOCs in the atmosphere and in indoor environments and determine the variation in total VOC (TVOC) concentration with time, respectively. In the Peak Capture System, real time monitoring was used to predict future elevations in the TVOC concentration (peak), and this was used an indicator of when to collect (capture) ambient air samples for integration analysis. This enabled qualitative and quantitative analysis of VOCs when the TVOC concentration was high. We developed an algorithm to predict variation in the TVOC concentration, and constructed an automatic system to initiate air sampling for integration analysis. With the system, auto-sampling and analysis of VOCs in a conventional house were conducted. In comparison with background concentrations, the results of peak analysis enabled identification of compounds whose concentration rose. This also enabled an evaluation of possible VOC emission sources.

Measurements of Volatile Organic Compounds in a Newly Built Daycare Center

We measured temporal changes in concentrations of total volatile organic compounds (TVOCs) and individual volatile organic compounds in a newly built daycare center. The temporal changes of the TVOC concentrations were monitored with a photo ionization detector (PID), and indoor air was sampled and analyzed by Gas Chromatography/Mass Spectrometry (GC/MS) and high performance liquid chromatography (HPLC) to determine the concentrations of the constituent VOCs. The measurements were performed just after completion of the building and again 3 months after completion. The TVOC concentration exceeded 1000 µg·m−3 for all the sampling locations just after completion of building, and decreased almost one tenth after 3 months, to below the guideline values of the TVOC in Japan at 400 µg·m−3. The concentrations of the target VOCs of which the indoor concentrations are regulated in Japan were below the guideline values for all the cases. The air-exchange rates were determined based on the temporal changes of the TVOC concentrations, and it was found that the countermeasure to increase the air exchange rate successfully decrease the TVOC concentration level in the rooms.

Dissolution of CO2 droplets in the ocean

Dissolution of CO2 droplets in the ocean has been studied. Owing to hydrogen bonding and supersaturation with CO2, seawater at the surface of the CO2 droplets becomes highly structured. Since this quasi-crystalline structure is similar to that of hydrate crystal elements, hydrate formation on the droplets will not cause a dramatic decrease in the dissolution rate as reported in the literature. Mass transfer of a buoyant CO2 droplet in Stokes flow in the ocean is analyzed. Based on the derived mass-transfer coefficients, shrinkage rates for CO2 droplets without and with a hydrate shell are predicted. Good agreement is observed between predictions and experimental data.