Batch processes cross flow

A flow diagram of a simple cross-flow system is shown in Figure 16.12. This is the system likely to be used for batch processing or development rigs it is in essence a basic pump recirculation loop. The process feed is concentrated by pumping it from the tank and across the membrane in the module at an appropriate velocity. The partly concentrated retentate is recycled into the tank for further processing while the permeate is stored or discarded as required. In cross-flow filtration applications, product washing is frequently necessary and... 

Metal-catalyzed cross-couplings are key transformations for carbon-carbon bond formation. The applicability of continuous-flow systems to this important reaction type has been shown by a Heck reaction carried out in a stainless steel microreactor system (Snyder et al. 2005). A solution of phenyliodide 5 and ethyl acrylate 6 was passed through a solid-phase cartridge reactor loaded with 10% palladium on charcoal (Scheme 2). The process was conducted with a residence time of 30 min at 130°C, giving the desired ethyl cinnamate 7 in 95% isolated yield. The batch process resulted in 100% conversion after 30 min at 140°C using a preconditioned catalyst. 

Even if the problems of poor crystal intergrowth due to local exhaustion of reactants in the autoclave and synthesis of zeolite material in the bulk of the solution were solved, an important problem remains, related to the fact that several batch synthesis cycles (with their associated heating and cooling processes) are often required to achieve a zeolite membrane of good quality. Thus, a synthesis procedure in which reactants are continuously supplied to the synthesis vessel while this is maintained at a constant temperature would clearly be desirable not only for performance but also for the feasibility of the scale-up. This type of approaches has already been tested for inner MFI and NaA zeolite membranes [33-35], and the results obtained indicate that the formation of concomitant phases and the amount of crystals forming in the liquid phase are greatly reduced. Similarly, the continuous seeding of tubular supports by cross-flow filtration of aqueous suspensions [36-37] has been carried out for zeolite NaA membrane preparation. 

Like enzymes, whole cells are sometimes immobilized by attachment to a surface or by entrapment within a support. One motivation for this is similar to the motivation for using biomass recycle in a continuous process. The cells are grown under optimal conditions for cell growth but are used at conditions optimized for production of a secondary metabolite. A hollow-liber reactor, similar to those used for cross-flow filtration, can be used to entrap the cells while allowing input of the substrate and removal of products. Attachment of the cells to a nonreactive material such as alumina allows a great variety of reactor types including packed beds, fluidized and spouted beds, and air-lift reactors. Packed beds with a biofilm on the packing are commonly used for wastewater treatment. A semicommercial process for beer used an air-lift reactor to achieve reaction times of one day compared to five to seven days for the normal batch process. Unfortunately, the beer suffered from a mismatched flavor profile that was attributed to mass transfer limitations. 

The following formulation illustrates the use of a redox initiator in a batch process. Also, the introduction of A-methylol acrylamide increases the molecular weight and chain cross-linking, minimizing the thermoplastic properties of the adhesive and the tendency to cold flow. 

Cross-flow systems typically operate at constant pressure and not at constant flux. The design and mode of operation of UF and MF systems are defined by the process needs and application. There are three main process configurations (a) single-pass, (b) batch filtration, and (c) feed-and-bleed [34,48]. By contrast, aU RO and NF systems are of single-pass design. Batch and feed-and-bleed designs involve extensive recycling to... 

Figure 2.28 Typical process configurations of UF/MF cross-flow systems (a) single pass, (b) batch process, and (c) feed-and-bleed.

Cross-flow MF and UF can be operated in different configurations, depending on the requirements of the process. Commonly used modes of operation are total recycle, batch concentration, feed-and-bleed and diafiltration (Cheryan, 1998 Ho and Sirkar, 1992). 

Polyurea microcapsules containing Pd(OAc)2 (Pd EnCat ) have been used in Suzuki-Miyaura cross-coupling processes conducted in either batch or continuous-flow mode. ... 

There are a number of phase equilibrium driven separation processes where the separation devices are such that crossflow of two bulk phases exists. Crossflow is utilized to enable continuous contacting between two immiscible phases, vapor and liquid, in an efficient fashion, as in a plate located in a distillation column. In chromatographic processes, crossflow of the solid adsorbent particles and the mobile fluid phase (liquid or gas) can lead to continuous separation of a multicomponent feed mixture introduced at one location of the mobile fluid (eluent) phase. We will illustrate first how crossflow of adsorbent particles or the adsorbent bed and the mobile fluid phase overcomes the batch nature of multicomponent separation in elution chromatography. Then we will focus on the cross-flow plate in a distillation column. 

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