On the other hand, a prio3'i criteria have been reported recently (Huang and Varma 1981a) applying the fast pseudofirst-order reacnon model (model If) in a nonadiabatic gas-liquid CSTR to provide necessary and sufficient conditions among physico-chemical parameters which assure unique and multiple steady states, and also the asymptotic stability of the steady states. It is believed that these a priori criteria can be derived only by assuming the pseudo-first-order reaction in the "fast" reaction regime (i. e . , the fast pseudo-first-order reaction model). Therefore, the use of' the fast pseudo-first-order reaction model is justifiable not only because of the fair agreement between the multiplicity regions predicted by this model and the second-order reaction model, but also because of its capability to lead to a priori criteria, as shown by the analyticity of the uniqueness and multiplicity regions presented in this work.Thus, it is recommended that the fast pseudo-first-order reaction model (model If) be always applied first to give an idea of the multiplicity regions of second-order reactions; if specific operational conditions are close to regions of multiplicity predicted by this model, then a fine tuning can be done to identify the possibility precisely by using the pseudo-first-order reaction model (model 1) and the full second-order reaction model (model 2)-in that order. Although both models 1 and 2 use trial-and-error, the computational effort is significantly lower for model 1.

Annular c e n t r i f u g a l c o n t a c t o r s s u i t a b l e f o r l a b o r a t o r y use i n s o l v e n t e x t r a c t i o n work have been designed and t e s t e d f o r b o t h h y d r a u l i c performance and m a s s -t r a n s f e r e f f i c i e n c y . The 2-cm c o n t a c t o r s have nominal flow r a t e s of 80 mL/min and m a s s -t r a n s f e r e f f i c i e n c i e s of a t l e a s t 85% a s measured by t h e e x t r a c t i o n of uranium. These c o n t a c t o r s work w e l l f o r organicto-aqueous (O/A) flow r a t i o s g r e a t e r than 0.8. M u l t i s t a g e u n i t s a l l o w proposed flow s h e e t s t o be t e s t e d on a c o n t i n u o u s b a s i s i n t h e l a b o r a t o r y .Scale-up t o l a r g e r p l a n t -s i z e u n i t s i s s t r a i g h tforward.

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Polymer self-assembly leading to cooling-induced hydrogel formation is relatively rare for synthetic polymers and typically relies on H-bonding between repeat units. Here, we describe a non-H-bonding mechanism for a cooling-induced reversible order−order (sphere-to-worm) transition and related thermogelation of solutions of polymer self-assemblies. A multitude of complementary analytical tools allowed us to reveal that a significant fraction of the hydrophobic and hydrophilic repeat units of the underlying block copolymer is in close proximity in the gel state. This unusual interaction between hydrophilic and hydrophobic blocks reduces the mobility of the hydrophilic block significantly by condensing the hydrophilic block onto the hydrophobic micelle core, thereby affecting the micelle packing parameter. This triggers the order−order transition from well-defined spherical micelles to long worm-like micelles, which ultimately results in the inverse thermogelation. Molecular dynamics modeling indicates that this unexpected condensation of the hydrophilic corona onto the hydrophobic core is due to particular interactions between amide groups in the hydrophilic repeat units and phenyl rings in the hydrophobic ones. Consequently, changes in the structure of the hydrophilic blocks affecting the strength of the interaction could be used to control macromolecular self-assembly, thus allowing for the tuning of gel characteristics such as strength, persistence, and gelation kinetics. We believe that this mechanism might be a relevant interaction pattern for other polymeric materials as well as their interaction in and with biological environments. For example, controlling the gel characteristics could be considered important for applications in drug delivery or biofabrication.