Removal of trichloroethylene and trichloroethane using a novel hollow-fibre gas-permeable membrane

In order to evaluate effects of operational parameters on the removal efficiency of trichloroethylene and 1,1,1-trichloroethene from water, lab-scale experiments were conducted using a novel hollow-fibre gaspermeable membrane system, which has a very thin gas-permeable membrane held between microporous support membranes. The permeation rate of chlorinated hydrocarbons increased at higher temperature and water flow rate. On the other hand, the effects of the operational conditions in the permeate side were complex. When the permeate side was kept at low pressure without sweeping air (pervaporation), the removal efficiency of chlorinated hydrocarbon, as well as water permeation rate, was low probably due to lower level of membrane swelling on the permeate side. But when a very small amount of air was swept on the membrane (air perstripping) under a low pressure, it showed a higher efficiency than in any other conditions. Three factors affecting the permeation rate are: 1) reduction of diffusional boundary layer within the microporous support membrane, 2) air/vapour flow regime and short cutting, and 3) the extent of membrane swelling on the permeate side. A higher air flow, in general, reduces the diffusional boundary layer, but at the same time disrupts the flow regime, causes short cutting, and makes the membrane dryer. Due to these multiple effects on gas permeation, there is an optimum operational condition concerning the vacuum pressure and the air flow rate. Under the optimum operational condition, the residence time within the hollow-fibre membrane to achieve 99% removal of TCE was 5.25 minutes. The log (removal rate) was linearly correlated with the average hydraulic residence time within the membrane, and 1 mg/L of TCE can be reduced to 1 μg/L (99.9% removal).

Dyeing Rate of Nylon 6 Fabric and Yarn Assemblies with p-Aminoazobenzene

The dyeing rates of p-aminoazobenzene on nylon 6 fabrics and yarn assemblies at 40°C have been investigated. The apparent diffusion coefficient and the diffusional boundary layer parameter are estimated in such a way that the experimental data fit the theoretical rate curve based on the diffusional boundary layer model. Because the boundary layer parameter can be separated into two distinct components, the relationship between each component and the dyeing condition and the structure of the textile assembly is examined. The component concerned with the dye-fiber-dyebath combination or composition is subdivided into several groups. The component determined by the fluid-flow pattern and rate is dependent on the magnitude of the inter-yarn spaces.

Dyeing Rate of Nylon 6 Yarn with p-Aminoazobenzene

The dyeing rate of p-aminoazobenzene on nylon 6 yarn at 40°C has been investigated. The apparent diffusion coefficient and the diffusional boundary layer parameter are estimated in such a way that the experimental data fit with the theoretical rate curve based on the diffusional boundary layer model. The dyeing behavior of the yarn is discussed in relation to the pore size of the spaces between individual filaments.

Diffusion of an Acid Dye in a Multiple Porous Membrane Assembly

We have investigated the concentration distribution of an acid dye in a multiple porous cellulosic membrane. On the basis of the diffusional boundary layer model, we present the computational method of a concentration-dependent diffusion coefficient of dye in multiple layers. We have assumed that the relationship between the diffusion coefficient Df and the dye concentration C is of the form Df = Dfo exp(α C). The concentration-dependent diffusion coefficient estimated by the numerical method is in close agreement with that predicted by the pore model in a dye concentration range of about 1.0 to 2.2 × 10−2 mol/kg.