Reactive Separation Processes

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... 

Kulprathipanja, S. (2002) Reactive Separation Process, Taylor Francis, New York, USA. 

Reactive absorption is probably the most widely applied type of a reactive separation process. It is used for production purposes in a number of classical bulk-chemical technologies, such as nitric or sulfuric acid. It is also often employed in gas purification processes, e.g., to remove carbon dioxide or hydrogen sulfide. Other interesting areas of application include olefin/paraffin separations, where reactive absorption with reversible chemical complexation appears to be a promising alternative to the cryogenic distillation (62). 

The most important examples of reactive separation processes (RSPs) are reactive distillation (RD), reactive absorption (RA), and reactive extraction (RE). In RD, reaction and distillation take place within the same zone of a distillation column. Reactants are converted to products, with simultaneous separation of the products and recycling of unused reactants. The RD process can be efficient in both size and cost of capital equipment and in energy used to achieve a complete conversion of reactants. Since reactor costs are often less than 10% of the capital investment, the combination of a relatively cheap reactor with a distillation column offers great potential for overall savings. Among suitable RD processes are etherifications, nitrations, esterifications, transesterifications, condensations, and alcylations (2). 

This chapter concerns the most important reactive separation processes reactive absorption, reactive distillation, and reactive extraction. These operations combining the separation and reaction steps inside a single column are advantageous as compared to traditional unit operations. The three considered processes are similar and at the same time very different. Therefore, their common modeling basis is discussed and their peculiarities are illustrated with a number of industrially relevant case studies. The theoretical description is supported by the results of laboratory-, pilot-, and industrial-scale experimental investigations. Both steady-state and dynamic issues are treated in addition, the design of column internals is addressed. 

Despite the recent rapid development of computer technology and numerical methods, the rate-based approach in its current realization still often requires a significant computational effort, with related numerical difficulties. This is one of the reasons the application of rate-based models to industrial tasks is rather limited. Therefore, further work is required in order to bridge this gap and provide chemical engineers with reliable, consistent, robust, and comfortable simulation tools for reactive separation processes. 

Noeres C, Kenig EY, Gorak A. Modelling of reactive separation processes reactive absorption and reactive distillation. Chem Eng Process 2003 42 157-178. 

Higler AP, Krishna R, Taylor R. Nonequilibrium-cell model for multicomponent (reactive) separation processes. AIChE J 1999 45 2357-2370. 

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. 

Section 4.3 elucidates the role of vapor-liquid mass transfer resistances on the feasible products of nonreactive or reactive separation processes. The latter are considered under chemical equilibrium conditions (i.e., they are very fast reactions). The feasible products are denoted as arheotropes. 

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. 

If a very fast reaction is considered, the reactive separation process can be satisfactorily described assuming reaction equilibrium. Here, a proper modeling approach is based on the non-reactive equilibrium stage model, extended by simultaneously... 

This paper gives a comprehensive review of the up-to-date modeling of reactive separation processes in columns equipped with structured packings and consider in detail two different modeling ways. The first approach is based on the application of CFD, whereas the second one employs the idea of hydrodynamic analogy between complex and simple flow patterns. 

The mathematical model comprises a set of partial differential equations of convective diffusion and heat conduction as well as the Navier-Stokes equations written for each phase separately. For the description of reactive separation processes (e.g. reactive absorption, reactive distillation), the reaction terms are introduced either as source terms in the convective diffusion and heat conduction equations or in the boundary condition at the channel wall, depending on whether the reaction is homogeneous or heterogeneous. The solution yields local concentration and temperature fields, which are used for calculation of the concentration and temperature profiles along the column. 

Egorov, Y., Menter, F., Kloeker M., Kenig, E.Y. On the combination of CFD and rate-based modelling in the simulation of reactive separation processes. Chem. Eng. Process., Vol. 44, 631-644, 2005. 

Carr, R. W., Dandekar, H. W. Adsorption with reaction, in Reactive Separation Processes, Kulp-rathipanja, S. (Ed.), Taylor Francis, New York, 2002. 

Reactive separation processes are of significant industrial importance owing to the potential opportunities in generating novel products and their substantial technical and commercial advantages. Some of the advantages of conducting reaction and separation simultaneously include ... 

The term reactive distillation (RD) refers to both catalyzed and uncatalyzed reaction systems. Catalytic distillation systems may use a homogenous or heterogenous catalyst to accelerate the reaction. Reactive distillation is a well-known example of reactive separation process, and is used commercially. The first patent and early journal articles deal mainly with homogenously catalyzed reactions such as esterifications, transesterifications, and hydrolysis.f Heterogenous catalysis with RD is a more recent development. The key advantages for a properly designed RD colunm are complete conversion of reactants and attainment of high selectivity. An example of the benefits of RD is the acid catalyzed production of methyl acetate by... 

Kulprathipanja, S., Ed. Reactive Separation Processes Taylor Francis Philadelphia, 2001. 

Towler, G.P. Frey, S.J. Reactive distillation. In Reactive Separation Processes Kulprathi-panja, S., Ed. Taylor Francis Philadelphia, 2001. 

Engell, S. Fernholz, G. Control of a reactive separation process. Chem. Eng. Process. 2003, 42, 201-210. 

Solvent extraction is widely used in pharmaceutical and food processing industries. Oil seed extraction, manufacturing of neutraceuticals, decaffeinated coffee, intermediates, and some reactive-separation processes utilize solvent extraction. Hydrocarbons are common solvents for oil seed extraction. Supercritical solvents are gaining popularity in producing neutraceuticals and other active ingredients. 

The first case deals with multifunctional equipment that couples or uncouples elementary processes (transfer-reaction-separation) to increase productivity and/or selectivity with respect to the desired product and to facilitate the separation of undesired by-products. Numerous reactive separation processes involving unit operation hybridization exist. 

V. van Brunt, J. S. Kanel, in Reactive Separation Processes, Taylor Francis/ London, 2002, Chapter 3,51. 

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. 

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. 

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