Reactive separation membranes

Melt-state testing, of polymers, 19 575 Melt-to-mold thermoforming, 18 49 Melt viscosities (MVs), 21 712-714 of ethylene oxide polymers, 10 680 of FEP resin, 18 306, 308 Membrane-based reactive separation processes, 15 848... 

Reactive distillation Membrane-based reactive separations Reactive adsorption Reactive absorption Reactive extraction Reactive crystallization... 

DOE has cofunded lactic acid separations technology involving the use of electro dialysis, advanced membranes, and reactive separations capable of converting the lactic acid salts made during fermentation directly into ethyl lactate. 

Today, there is an increasing interest in the theoretical study and the practical application of integrated reactive separation processes such as reactive distillation columns [1-3] or membrane-assisted reactors [37]. However, to date there is no general method available for designing such processes. For practical applications, it is important to be able to evaluate quickly whether a certain reactive separation process is a suitable candidate to reach certain targets. Therefore, feasibility analysis tools being based on minimal thermodynamic and kinetic information of the considered system are valuable. 

As demonstrated by means of residue curve analysis, selective mass transfer through a membrane has a significant effect on the location of the singular points of a batch reactive separation process. The singular points are shifted, and thereby the topology of the residue curve maps can change dramatically. Depending on the structure of the matrix of effective membrane mass transfer coefficients, the attainable product compositions are shifted to a desired or to an undesired direction. 

Sungpet A, Way JD, Thoen PM, and Dorgan JR. Reactive polymer membranes for ethylene/ethane separation. J Membr Sci 1997 136 111-120. 

Membrane-based reactive separation processes, which seek to combine two distinct functions, i.e. reaction and separation, have been around as a concept since the early stages of the membrane field, itself, but have only attracted substantial technical interest during the last decade or so [1.22]. There is ongoing significant industrial interest in these processes, because they promise to be compact and less capital intensive, and because of their promise for potential substantial savings in the processing costs [1.23]. 

Membrane-based reactive separation processes (also known as membrane reactor processes) are attracting attention in catalytic reactor applications. In these reactor systems the membrane separation process is coupled with a catalytic reaction. When the separation and reaction processes are combined into a single unit the membrane, besides providing... 

J. Sanchez and T.T. Tsotsis, Reactive Membrane Separation , in Reactive Separation Processes, S. Kulprathipanja, Ed., Taylor Francis, USA, 2001. 

More promising for reactive separations involving gas phase reactions appears to be the development and use in such applications of microporous zeolite and carbon molecular sieve (Itoh and Haraya [2.25] Strano and Foley [2.26]) membranes. Zeolites are crystalline microporous aluminosilicate materials, with a regular three-dimensional pore structure, which are relatively stable to high temperatures, and are currently used as catalysts or catalyst supports for a number of high temperature reactions. One of the earliest mentions of the preparation of zeolite membranes is by Mobil workers (Haag and Tsikoyiannis... 

Another partial oxidation reaction that is attracting industrial attention for the application of reactive separations is the production of synthesis gas from methane [Stoukides, 2.127]. The earlier efforts made use of solid oxide solutions as electrolytes. Stoukides and coworkers (Eng and Stoukides [2.200, 2.126], Alqahtany et al. [2.201, 2.202]), for example, using a YSZ membrane in an electrochemical membrane reactor obtained a selectivity to CO and H2 of up to 86 %. They found that a Fe anodic electrode was as active as Ni in producing synthesis gas from methane (Alqahtany et al. [2.201, 2.202]), and that electro-chemically produced O was more effective in producing CO than gaseous oxygen (no ef-... 

Pervaporation membrane reactors (PVMR) are an emerging area of membrane-based reactive separations. An excellent review paper of the broader area of pervaporation-based, hybrid processes has been published recently [3.1]. The brief discussion here is an extract of the more comprehensive discussions presented in that paper, as well as in an earlier paper by Zhu et al [3.2]. Mostly non-biological applications are discussed in this chapter. Some pervaporation membrane bioreactor (PVMBR) applications are also discussed additional information on the topic can be found in a recent publication [3.3], and a number of other examples are also discussed in Chapter 4. 

Groot et al [3.86] investigated the technical feasibility of five reactive separation technologies (fermentation coupled to stripping, adsorption, liquid-liquid extraction, pervaporation, and membrane solvent extraction). They concluded that liquid-liquid extraction and pervaporation reactive separation processes show the greatest potential, with PVMBR systems particularly attractive due to their operational simplicity. Membranes utilized include silicone [3.76, 3.77, 3.74, 3.87, 3.75, 3.85, 3.88], supported liquid membrane systems [3.87, 3.89], polypropylene [3.70], and silicalite filled PDMS membranes [3.90, 3.91]. The results with PVMBR systems have been very promising. 

The above examples have shown that pervaporation membrane-based reactive separation processes are attracting significant attention and that the technology has found some industrial applications. This is an area, where significant activity is already under way, and many more advances are expected in the future. 

Membrane-based reactive separation (otherwise also known as membrane reactor) processes, which constitute the subject matter of this book, are a special class of the broader field of membrane-based separation processes. In this introduction we will first provide a general and recent overview on membranes and membrane-based separation processes. The goal is to familiarize those of our readers, who are novice in the membrane field, with some of the basic concepts and definitions. A more complete description on this topic, including various aspects of membrane synthesis can be obtained from a number of comprehensive books and reviews that have already been published in this area [1.1, 1.2, 1.3,... 

We will then follow in this introduction with an outline of some of the generic aspects of the field of membrane-based reactive separations, which our reader will, hopefully, find useful while navigating through the rest of this book. 

Process intensifying methods, such as the integration of reaction and separation steps in multifunctional reactors (examples reactive distillation, membrane reactors, fuel cells), hybrid separations (example membrane distillation), alternative energy sources, and new operation modes (example periodic operations). 

Hyflon AD amorphous fluoropolymer is used in optical devices, pellicles in semiconductor manufacture, as a dielectric and as a separation membrane. Small amounts of TDD have been used as a modifier in ethylene-chlorotrifluoroethylene polymers to increase stress crack resistance. Minute amounts of TDD are used also as a modifier in polytetrafluoroethylene to improve elastic modulus, reduce creep and permeability and increase transparency. It has been suggested that the much higher reactivity of TDD and other fluorinated dioxoles relative to other modifiers gives a more uniform distribution of the modifier in the polymer chain that results in a greater increase in the desired properties at lower concentration of modifier in the polymer. 

Today, RD is discussed as one part of the broader area of reactive separation, which comprises any combination of chemical reaction with separation such as distillation, stripping, absorption, extraction, adsorption, crystallization, and membrane separation. In the next decade, unifying approaches to reactive separators should be developed allowing the rigorous selection of the most suitable type of separation to be integrated into a chemical reactor. 

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