Hybrid process reactors

A CVD reaction can occur in one of two basic systems the closed reactor or the open reactor (also known as close or open tube). The closed-reactor system, also known as chemical transport, was the first typetobeusedforthe purification of metals. It is a hybrid process which combines vapor-phase transfer with solid-state diffusion. As the name implies, the chemicals are loaded in a container which is then tightly closed. A temperature differential is then applied which provides the driving force for the reaction. 

Rinard dedicated his research to a detailed analysis of methodological aspects of a micro-reactor plant concept which he also termed mini-plant production [85] (see also [4, 9, 10] for a commented, short description). Important criteria in this concept are JIT (Just-in-time) production, zero holdup, inherent safety, modularity and the KISS (keep it simple, stupid) principle. Based on this conceptual definition, Rinard describes different phases in plant development. Essential for his entire work is the pragmatic way of finding process solutions, truly of hybrid character ]149] (miniaturization only where really needed). Recent investigations are concerned with the scalability of hybrid micro-reactor plants and the limits thereof ]149], Expliddy he recommends jointly using micro- and meso-scale components. 

For continuous processes the catalytic reactor, or a hybrid process if satisfactory chemical dosing equipment is already installed, appear to be a near-optimum solution still for many installations. At moderate hypochlorite concentrations, economic benefit does accrue from using the catalyst in-loop rather than end-of-pipe, but these benefits may be offset by any required investment in heat-exchange capability. At concentrations above 10 wt% the integration of decomposition into the scrubbing process is beneficial to the overall cost base of hypochlorite treatment. 

Another area where membrane reactors have now reached the industrial scale is in pervaporation-based hybrid processes using various types of polymer membranes (for an informative review, see Ref. [78]). 

Howell JA. Future of membranes and membrane reactors in green technologies and for water reuse. Desalination, 2004 162(10) 1-11. Noronha M, Britz T, Mavrov V, Janke HD, and Chmiel H. Treatment of spent process water from a fruit juice company for purposes of reuse Hybrid process concept and on-site test operation of a pilot plant. Desalination, 2002 143(2) 183-196. 

In hybrid processes, membranes are used to remove end-product from the reactor, allowing a chemical or a biochemical reaction to carry on. Hybrid membrane... 

Polymeric membranes also show potential for application in the area of chiral catalysis. Here metallocomplexes find use as homogeneous catalysts, since they show high activity and enantioselectivity. They are expensive, however, and their presence in the final product is undesirable they must be, therefore, separated after the reaction ends. Attempts have been made to immobilize these catalysts on various supports. Immobilization is a laborious process, however, and often the catalyst activity decreases upon immobilization. An alternative would be a hybrid process, which combines the homogeneous catalytic reactor with a nanofiltration membrane system. Smet et al. [2.98] have presented an example of such an application. They studied the hydrogenation of dimethyl itaconate with Ru-BINAP as a homogeneous chiral catalyst. The nanofiltration membrane helps separate the reaction products from the catalyst. Two different configurations can be utilized, one in which the membrane is inserted in the reactor itself, and another in which the membrane is extraneous to the reactor. Ru-BINAP is known to be an excellent hydrogenation catalyst... 

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. 

Catalytic Pyrolysis Catalytic pyrolysis has been studied as a hybrid process for recovering caprolactam from nylon 6 followed by high-temperature pyrolysis of the polypropylene into a synthetic natural gas. Czemik et al. [27] investigated the catalysis of the thermal degradation of nylon 6 with an a-alumina supported KOH catalyst in a fluidized-bed reactor. In the temperature range of 330-360°C the yield of caprolactam exceeded 85%. 

Pervaporation, as a non-integrated process, is typically utilized for dehydration and for the recovery or removal of organics from aqueous solutions and sometimes also for the separation of organic mixtures (Neel, 1995). Also many hybrid processes have been developed where PV is coupled with other processes, such as different membrane processes (e.g., reverse osmosis, or organophilic pervaporation coupled with hydrophilic pervaporation), distillation, reactive distillation and, of course, reaction. With these aspects in mind, PV appears particularly suitable to keep the concentration of a by-product low, or to continuously recover a product while it is formed. Note that these are the main objectives typically pursued in membrane reactors. 

In order to fully exploit this catalyst system a unique commercial polymerization process was developed, Himont s Spheripol process is, in practice, a two-stage hybrid process consisting of both liquid and gas phases. Homopolymerization takes place in the liquid slurry phase, and after removal of unreacted monomer and solvent, the solid, porous particles pass into the gas phase part of the process in which the introduction of other monomers allows copolymerization to take place within the solid, spherical particle. This growing polymer particle has become a "reactor granule" and represents a revolution in the development of Ziegler-Natta catalysis. Since polymerization can take place within a solid polymer shell, the mechanical containment aspects of the polymerization process became secondary. Bulk, gas phase, and slurry processes are all equally adaptable for use with this catalyst system and are chosen based on economics, mechanical reliability and reaction control criteria in order to maximize reactivity and productivity. It removes almost all of the previous process constraints on Ziegler-Natta catalysis, allowing reactor-made resins to be produced with... 

With the formation of ester and water the rate of reaction slows down with time. It takes 24-36 h to process 25,000- 30,000 L/day. Then it goes through a complex process to separate ester from the water and catalyst. The AZEO SEP hybrid process can breakdown the azeotrope of ethyl ester, ethanol, and water. After breaking down the azeotrope, it sends ethyl ester and unreacted ethanol back to the reactor to complete the reaction. This increases the yield of reaction significantly, and it reduces the reaction time two to threefold. 

Examples of different configurations for pervaporation inert membrane reactors, (a) External membrane unit (b) internal membrane unit and (c) hybrid process with external membrane unit and distillation column. (Adapted from van der Bruggen. Reprinted with permission from Elsevier, Copyright (2010).)... 

An improved solvent extraction process, PUREX, utilizes an organic mixture of tributyl phosphate solvent dissolved in a hydrocarbon diluent, typically dodecane. This was used at Savannah River, Georgia, ca 1955 and Hanford, Washington, ca 1956. Waste volumes were reduced by using recoverable nitric acid as the salting agent. A hybrid REDOX/PUREX process was developed in Idaho Falls, Idaho, ca 1956 to reprocess high bum-up, fuUy enriched (97% u) uranium fuel from naval reactors. Other separations processes have been developed. The desirable features are compared in Table 1. 

Hessel and Lowe report on hybrid, i.e. multi-scale, approaches which are currently most often favored for micro-reactor plant construction, simply for practical time and cost reasons [9, 10]. In addition, such an approach allows one to fit micro reactors in existing industrial, producing and academia, measuring environments. The micro reactor is only used where it is really needed and costs for changing the processing are kept to a minimum in such a way (Figure 1.9). 

The realization of complete bench-scale micro reactor set-ups is certainly still in its infancy. Nevertheless, the first investigations and proposals point at different generic concepts. First, this stems from the choice of the constructing elements for such set-ups. Either microfluidic components can be exclusively employed (the so-caUed monolithic concept) or mixed with conventional components (the so-called hybrid or multi-scale concept). Secondly, differences concerning the task of a micro-reactor plant exist. The design can be tailor-made for a specific reaction or process (specialty plant) or be designated for various processing tasks (multi-purpose plant). 

A micro reactor concept proposed by MIT and DuPont on the basis of electronic circuits is the most prominent among the examples listed for the hybrid approach [19,101]. The so-called turnkey multiple micro-reactor test station relies on the use of standard components originating from the semiconductor industry for microchemical processing, the construction being oriented at the concept of printed circuit boards. 

Vor dem Sprung in die Produktion, Chemie Produktion, December 2002 Prognoses on speed of implementation PAMIRmarket study industry s demands numbering-up risks expert opinions Clariant pigment micro-reactor production smallness not an end in itself general advantages of micro flow industrial process development and optimization share of reactions suited for micro reactors hybrid approach standardized interfaces start of industrial mass production of micro reactors unit construction kit [208],... 

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