Prediction of physico-chemical properties for PCs/DFs using the UNIFAC model with an alternative approximation for group assignment

The original-type UNIFAC model was used to predict the environmentally important physico-chemical properties of PCDDs/DFs, such as aqueous solubility, Henry's law constant, and 1-octanol/water partition coefficient, through the UNIFAC-derived infinite dilution activity coefficient. In this application, we suggest an alternative approximation that the aromatic ether group AC-O in PCDD/DF molecules is replaced with the aliphatic ether group CH-O, because the AC-O group is not available in the conventional UNIFAC model. With this approximation, the ability of the UNIFAC model to predict those properties was examined by comparing with experimental data. The UNIFAC model provided comparatively good estimation results. From these results, it is shown that the alternative approximation is useful for the UNIFAC estimation of physico-chemical properties for PCDDs/DFs. Furthermore, the predicted solubilities of 2,3,7,8-T4CDD and O8CDD in organic solvents and the co-solvency effect on solubility of PCDDs in methanol/water mixture indicate that the UNIFAC calculation presented here could well predict the physico-chemical properties of PCDDs/DFs in various solution conditions.     

Effects of pH on the water solubility and 1-octanol-water partition coefficient of 2,4,6-tribromophenol

2,4,6-Tribromophenol (TBP) is expected to exist in both ionic and non-ionic forms in the environment due to ionisation of the phenolic group at near neutral pH. In this study, the water solubility (Sw) and 1-octanol-water partition coefficient (Kow) of aqueous solutions of TBP at various pH values were measured using the shake flask method. The ionisation resulted in increasing Sw and decreasing Kow by two to three orders of magnitude. From the experimental results, the environmental partitioning characteristics of TBP and the effect of pH on partitioning were discussed through a comparison with the properties of tetrabromobisphenol A (TBBP-A), which has two phenolic groups. Furthermore, the pH dependence of Sw and Kow was represented using a Henderson-Hasselbalch type model and the validity of the model was evaluated. The model was found to be highly useful for predicting the pH dependence within the range of pH 3 to 9.     

Physicochemical properties of selected polybrominated diphenyl ethers and extension of the UNIFAC model to brominated aromatic compounds

The aqueous solubilities (S(w)) at various temperatures from 283 K to 308 K and 1-octanol/water partition coefficients (K(ow)) for four polybrominated diphenyl ethers (PBDEs: 4,4'-dibromodiphenyl ether (BDE-15), 2,2',4,4'-tetrabromodiphenyl ether (BDE-47), 2,2',4,4',5-pentabromodiphenyl ether (BDE-99), and 2,2',4,4',5,5'-hexabromodiphenyl ether (BDE-153)) were measured by the generator column method. The S(w) and K(ow) data revealed the effect of bromine substitution and basic structure on S(w) and K(ow). To estimate the infinite dilution activity coefficients (gamma(i)(w,infinity)) of the PBDEs in water from the S(w) data, enthalpies of fusion and melting points for those compounds were measured with a differential scanning calorimeter. Henry's Law constants (H(w)) of the PBDEs were derived from the determined gamma(i)(w,infinity) and literature vapor pressure data. Some physicochemical characteristics of PBDEs were also suggested by comparing the present property data with that of polychlorinated dibenzo-p-dioxins, brominated phenols and brominated benzenes in past studies. Furthermore, in order to represent different phase equilibria including solubility and partition equilibrium for other brominated aromatic compounds using the UNIFAC model, a pair of UNIFAC group interaction parameters between the bromine and water group were determined from the S(w) and K(ow) data of PBDEs and brominated benzenes. The ability of the determined parameters to represent both properties of brominated aromatics was evaluated.     

Prospects for cost-effective post-combustion CO2 capture from industrial CHPs

Industrial Combined Heat and Power plants (CHPs) are often operated at partial load conditions. If CO₂ is captured from a CHP, additional energy requirements can be fully or partly met by increasing the load. Load increase improves plant efficiency and, consequently, part of the additional energy consumption would be offset. If this advantage is large enough, industrial CHPs may become an attractive option for CO₂ capture and storage CCS. We therefore investigated the techno-economic performance of post-combustion CO₂ capture from small-to-medium-scale (50–200 MWe maximum electrical capacity) industrial Natural Gas Combined Cycle- (NGCC-) CHPs in comparison with large-scale (400 MWe) NGCCs in the short term (2010) and the mid-term future (2020–2025). The analyzed system encompasses NGCC, CO₂ capture, compression, and branch CO₂ pipeline.The technical results showed that CO₂ capture energy requirement for industrial NGCC-CHPs is significantly lower than that for 400 MWe NGCCs: up to 16% in the short term and up to 12% in the mid-term future. The economic results showed that at low heat-to-power ratio operations, CO₂ capture from industrial NGCC-CHPs at 100 MWe in the short term (41–44 €/tCO₂ avoided) and 200 MWe in the mid-term future (33–36 €/tCO₂ avoided) may compete with 400 MWe NGCCs (46–50 €/tCO₂ avoided short term, 30–35 €/tCO₂ avoided mid-term).     

Predicted distribution of 16 short-chain chlorinated paraffins in air,water, soils and sediments

Environmental Chemistry Letters - Short-chain chlorinated paraffins are industrial contaminants of great concern due to their persistent and toxic characteristics. The predicted distribution of...     

The G20 emission projections to 2030 improved since the Paris Agreement,but only slightly

Mitigation and Adaptation Strategies for Global Change - Climate adaptation is seen by many as increasingly important and as deeply political, leading some to argue for its democratization. Social...     

Hydrogen-rich synthesis gas production from waste wood via gasification and reforming technology for fuel cell application

The purpose of this study was to establish a fuel process for an advanced power generation system in which hydrogen-rich synthesis gas, as the fuel for the molten carbonate fuel cell (MCFC), can be extracted from biomass via gasification and reforming technologies. Experiments on waste wood gasification were performed using a bench-scale gasification system. The main factors influencing hydrogen generation in the noncatalytic process and in the catalytic process were investigated, and temperature was identified as the most important factor. At 950°C, without employing a catalyst, hydrogen-rich synthesis gas containing about 54 vol% hydrogen was extracted from feedstock with appropriately designed operation parameters for the steam/carbon ratio and the equivalence ratio. However, by employing a commercial steam reforming catalyst in the reforming process, similar results were obtained at 750°C.     

Assessment of river water quality during snowmelt and base flow periods in two catchment areas with different land use

River water quality was evaluated with respect to eutrophication and land use during spring snowmelt and summer base flow periods in Abashiri (mixed cropland-livestock farming) and Okoppe (grassland-based dairy cattle farming), eastern Hokkaido, Japan. Water from rivers and tributaries was sampled during snowmelt and summer base flow periods in 2005, and river flow was measured. Total N (TN), NO₃–N, and Si concentrations were determined using standard methods. Total catchment and upland areas for each sampling site were determined with ArcGIS hydrology modeling software and 1:25,000-scale digital topographic maps. Specific discharge was significantly higher during snowmelt than during base flow. In both areas, TN concentrations increased, whereas Si concentrations decreased, with increased specific discharge, and were significantly higher during snowmelt. The Si:TN mole ratio decreased to below or close to the threshold value for eutrophication (2.7) in one-third of sites during snowmelt. River NO₃–N concentrations during base flow were significantly and positively correlated with the proportion of upland fields in the catchment in both the Abashiri (r = 0.88, P < 0.001) and Okoppe (r = 0.43, P < 0.01) areas. However, the regression slope, defined as the impact factor (IF) of water quality, was much higher in Abashiri (0.025) than in Okoppe (0.0094). The correlations were also significantly positive during snowmelt in both areas, but IF was four to eight times higher during snowmelt than during base flow. Higher discharge of N from upland fields and grasslands during snowmelt and the resulting eutrophication in estuaries suggest that nutrient discharge during snowmelt should be taken into account when assessing and monitoring the annual loss of nutrients from agricultural fields.     

Evaluating stream water quality through land use analysis in two grassland catchments: impact of wetlands on stream nitrogen concentration

We evaluated the impacts of natural wetlands and various land uses on stream nitrogen concentration in two grassland-dominated catchments in eastern Hokkaido, Japan. Analyzing land use types in drainage basins, measuring denitrification potential of its soil, and water sampling in all seasons of 2003 were performed. Results showed a highly significant positive correlation between the concentration of stream NO3-N and the proportion of upland area in drainage basins in both catchments. The regression slope, which we assumed to reflect the impact on water quality, was 24% lower for the Akkeshi catchment (0.012 +/- 0.001) than for the Shibetsu catchment (0.016 +/- 0.001). In the Akkeshi catchment, there was a significant negative correlation between the proportion of wetlands in the drainage basins and stream NO3-N concentration. Stream dissolved organic nitrogen (DON) and carbon (DOC) concentrations were significantly higher in the Akkeshi catchment. Upland and urban land uses were strongly linked to increases in in-stream N concentrations in both catchments, whereas wetlands and forests tended to mitigate water quality degradation. The denitrification potential of the soils was highest in wetlands, medium in riparian forests, and lowest in grasslands; and was significant in wetlands and riparian forests in the Akkeshi catchment. The solubility of soil organic carbon (SOC) and soil moisture tended to determine the denitrification potential. These results indicate that the water environment within the catchments, which influences denitrification potential and soil organic matter content, could have caused the difference in stream water quality between the two catchments.     

Modification of UNIFAC parameter table Revision 5 for representation of aqueous solubility and 1-octanol/water partition coefficient for POPs

In order to represent aqueous solubility and 1-octanol/water partition coefficient for POPs (persistent organic pollutants) by the UNIFAC model, two pairs of group interaction parameters in Revision 5 of the UNIFAC parameter table were modified. First, the pair of interaction parameters between the aromatic carbon-chloride (ACCl) and water (H2O) groups were corrected by minimizing the deviation between the experimental and calculated values of these properties for chlorinated benzenes, polychlorinated biphenyls, and polychlorinated dibenzo-p-dioxins and dibenzofurans. The corrected interaction parameters provided a better representation of both properties than the calculation results obtained in early works using the UNIFAC model. Second, the unknown pair of interaction parameters between the chloroalkene (Cl(C=C)) and H2O groups, which are required for calculating those properties of the other five POPs (aldrin, chlordane, endrin, dieldrin, and heptachlor), were newly determined from the experimental data on their properties. Finally, this study shows that Revision 5 could also predict solubility of POPs in some organic solvents. The modified parameter table is first suggested as the UNIFAC parameter table applicable to various phase equilibria including aqueous or nonaqueous solubility and partition coefficient of POPs.