Long-term flux studies

Rahbari-Sisakht et al. [54] investigated the effect of novel surface modifying macromolecules (nSMMs) on the morphology and performance of PSf hollow-fiber membrane for CO2 absorption. The performance of surface-modifled membrane in contactor application for CO2 absorption through distilled water as absorbent was studied. The results show that surface-modified membrane had higher performance compared to plain polysulfone membranes. With the membrane prepared from SMM in the spinning dope, a maximum CO2 flux of 5.8 X 10 mol/m s was achieved at 300 ml/min of absorbent flow rate, which was almost 76% more than the other membrane. In a long-term stability study, the initial flux reduction was found to be about 18% after 50 h of operation of the surface-modified membrane. 

We speculate from the above argument that primordial sulfur degasses from midoceanic ridges even at present time as well as He, because subduction flux to mantle seems to be small. However, we need more detailed study on long-term S cycle including hydrothermal S flux to evaluate this speculation. 

The objective of the present study is to develop a cross-flow filtration module operated under low transmembrane pressure drop that can result in high permeate flux, and also to demonstrate the efficient use of such a module to continuously separate wax from ultrafine iron catalyst particles from simulated FTS catalyst/ wax slurry products from an SBCR pilot plant unit. An important goal of this research was to monitor and record cross-flow flux measurements over a longterm time-on-stream (TOS) period (500+ h). Two types (active and passive) of permeate flux maintenance procedures were developed and tested during this study. Depending on the efficiency of different flux maintenance or filter media cleaning procedures employed over the long-term test to stabilize the flux over time, the most efficient procedure can be selected for further development and cost optimization. The effect of mono-olefins and aliphatic alcohols on permeate flux and on the efficiency of the filter membrane for catalyst/wax separation was also studied. 

Transient and Steady-State Conditions From the landmine studies we readily conclude that the source term for these molecules has an initial spike, or increased rate, in the days or weeks after the mine is placed. This rate then decreases to some more or less constant level and may remain at that level for years. The initial spike comes from surface contamination, while the long-term rate is primarily from diffusion through the case and seals or leakage through imperfections or damage. The rates are clearly subject to environmental factors, principally temperature and soil wetness. Nevertheless, it seems clear that, at least in the case of landmines, there is a continuing flux of molecules that provide a potential for detection. 

Hellebrandt H.J. Kern J. and Scholz V. (2003). Long-term studies on greenhouse gas fluxes during cultivation of energy crops on sandy soils. Atmospheric Environment, 37(12), 1635-1644. 

For the BA waste, even if sensitivity ranking of ecotoxicity tests is similar, the evolution of ecotoxic hazard potential of the leachate fluxes was different between the two approaches. In the field, the ecotoxic hazard potential of leachate fluxes decreased, whereas it increased for the laboratory column study. The column approach tends to overestimate the long-term ecotoxic hazard potential of BA leachate fluxes generated in the field. This overestimation of the long-term ecotoxic hazard potential of leachate fluxes generated in the field may indicate that relevant factors such as 1) residence time of water in the waste, 2) the continuous or discontinuous watering of the waste and/or 3) the physico-chemical characteristics of the water used for obtaining leachates were not considered in the column approach. 

In this section, we will treat in more detail some critical properties related to membranes that are considered for use in C02 capture processes. As demonstrated in the previous section, the manner of membrane integration in the different processes has major implications for the operating working conditions. For a certain membrane type, the operational window is defined by the expected performance and stability. The flux and selectivity are mainly assessed on basis of short-term studies in model gases. The experience with real gases and long-term studies is limited, which is reflected in the assessments of critical issues given below. 

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