No abstract

A general model for the formation of thin-film composite membranes, that considers both diffusion- and reaction-controlled interfacial polymerization, under non-steady-state conditions, has been developed. Special models for either diffusion-controlled or reaction-controlled interfacial polymerization with steady- and non-steady-state conditions have been obtained by simplification; these agree with similar models, where available, in the literature. The porosity of the thin film is dependent on the amount of water that diffuses with the aqueous monomer into the formed film. The analytical solution for the model is consistent with the effect of diamine concentration and successfully predicts it for a polysulfonamide composite membrane fabricated from 1,2-ethanediamine and a disulfonyl chloride. The model allows simulation of various factors that affect thin-film formation, particularly for those factors that are difficult to measure experimentally. This work significantly extends existing theories and provides an important guide for effective control of the thickness of the surface barrier layer of thin-film composite membranes prepared by interfacial polymerization.

No abstract

is much more acceptable. This catalyst cost represents only the cost due to inability to recover the zinc and does not represent the costs involved in various recovery schemes.Following the hydrogenation step the zinc is distributed about equally between the liquid and solid products. In the liquid, the zinc is primarily, but not exclusively, in the water phase. The zinc content of the organic phase is greatly reduced by water washing. The zinc associated with the char is much more difficult to recover. Some of the char associated zinc is water soluble and even more is soluble in hydrochloric acid. Still more is rendered soluble by the use of cold concentrated nitric acid or hot 6 N nitric acid.Table V lists the overall recovery of the zinc catalyst by the application of two water rinse steps on the liquid portion and three different char treatment procedures for zinc removal. The first char treatment procedure, -combined with the water rinse treatment of the liquid, results in a 98.2% recovery of the zinc. The second char procedure represents a 99.0% recovery of the zinc, and the third a 98.3% recovery of the zinc. More stringent acid treatment procedures would result in more complete catalyst recovery, but at the expense of greater char oxidation. Because of the small scale of the operation, it has not been possible to make a realistic evaluation of the cost factors in catalyst recovery as yet.Literature Cited

Nonequilibrium molecular dynamics (NEMD) simulations are used to investigate pressure-driven water flow passing through carbon nanotube (CNT) membranes at low pressures (5.0 MPa) typical of real nanofiltration (NF) systems. The CNT membrane is modeled as a simplified NF membrane with smooth surfaces, and uniform straight pores of typical NF pore sizes. A NEMD simulation system is constructed to study the effects of the membrane structure (pores size and membrane thickness) on the pure water transport properties. All simulations are run under operating conditions (temperature and pressure difference) similar to a real NF processes. Simulation results are analyzed to obtain water flux, density, and velocity distributions along both the flow and radial directions. Results show that water flow through a CNT membrane under a pressure difference has the unique transport properties of very fast flow and a non-parabolic radial distribution of velocities which cannot be represented by the Hagen-Poiseuille or Navier-Stokes equations. Density distributions along radial and flow directions show that water molecules in the CNT form layers with an oscillatory density profile, and have a lower average density than in the bulk flow. The NEMD simulations provide direct access to dynamic aspects of water flow through a CNT membrane and give a view of the pressure-driven transport phenomena on a molecular scale.