Scale-up principle

The control of the deposition thickness is crucially important in the LCVD operation, regardless of the modes of operation. However, it is very difficult to measure the actual thickness of ultrathin film deposited on polymeric substrates. If an LCVD film is deposited on polymeric substrates, such as films, fibers, and molded articles, it is nearly impossible to determine the thickness by a simple nondestructive method that can be done quickly enough to monitor the LCVD operation. In order to circumvent this problem, the use of special substrates added or attached to the normal substrate is found to be satisfactory. A small piece of Si wafer is a typical case of this approach. Ellipsometer can measure the deposition on the Si wafer easily and quickly, which provides thickness and refractive index values. 

The large-scale operation should be conceptually built first, considering all requirements necessary to produce products in an industrial operation. The shape and nature of the substrate, e.g., continuous sheet of film or fibers, large or small disks, etc., dictate what kind of operation could be feasible in the industrial scale operation. From the conceptual operation, the key factors of LCVD process should be extracted, and then a laboratory scale reactor should be designed and constructed. In other words, a specific laboratory reactor should be built for a specific industrial scale operation. When this approach is followed, the scale-up of a successful laboratory operation is actually the scale-back to the original conceptual operation. 

On the scale-back process, the key factor is to not change the luminous gas phase as much as possible, which could be done by multiplying the unit process in the laboratory scale reactor in a larger volume vessel, instead of increasing the size of the unit process, e.g., the size of electrodes, the distance between electrodes, and so forth. 

Since the dissociation glow can be considered to be the major medium in which polymerizable species are created, the location of the dissociation glow, i.e., whether on the electrode surface or in the gas phase, has the most influence on where the most of the deposition by the plasma polymerization occurs. The deposition of plasma polymer could be divided into deposition E and deposition G as described in Chapter 8. The deposition kinetics is completely different for deposition E and deposition G. 

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Scale-Up Principles. Key factors affecting scale-up of reactor performance are nature of reaction zones, specific reaction rates, and mass- and heat-transport rates to and from reaction sites. Where considerable uncertainties exist or large quantities of products are needed for market evaluations, intermediate-sized demonstration units between pilot and industrial plants are usehil. Matching overall fluid flow characteristics within the reactor might determine the operative criteria. Ideally, the smaller reactor acts as a volume segment of the larger one. Elow distributions are not markedly influenced by... 

References 15 through 23 provide additional information on cyclone separators and the design and scale-up principles. 

References 29 through 38 provide additional information on filters and the design and scale-up principles. Note that vendors are some of the best sources of information on equipment. Look at some of the Web sites noted in this and other sections describing equipment. 

References 47 through 58 provide additional information on wet ESPs, design, and scale-up principles, as well as operational guidance. 

Gygax, R. W., "Scale-up Principles for Assessing Thermal Runaway Risks," Chem. Eng. Prog., 86,53 (February 1990). 

Gygax, R., "Explicit and Implicit Use of Scale-Up Principles for the Assessment of Thermal Runaway Risks in Chemical Production," in Proceedings of the International Symposium on Runaway Reactions, Center for Chemical Process Safety/AIChE, New York, NY (1989). 

Van Reis et al. [92] reported the scale-up of a HF system for the recovery of human tissue plasminogen activator (t-PA) produced by recombinant CHO cells from the 2.5-m to the 180-m scale. A robust and reproducible process was achieved by combining hnear scale-up principles, control of fluid dynamic parameters and experimentally defined limits of product retention, which meant maintaining channel length, wall shear rate and flux constant. 

Adaptability of an LCVD process in an industrial scale operation greatly depends on the nature of the onion structure of the luminous gas phase that could be accommodated in the operation. The change of reactor size inevitably changes the basic onion layer structure of the luminous gas phase, which constitutes the main (often insurmountable) difficulty in the scale-up attempt by increasing the size of reactor. (The scale-up principle is discussed in Chapter 19.)... 

The difference between well-known SCF antisolvent techniques such as GAS, PCA, and SEDS usually can be attributed to the specific nozzle mixing (or dispersing) technique involved. Enhanced mass and heat transfer can also be achieved by using mechanical and ultrasonic mixers and ultrafast jet expansion techniques. There are new developments for particle formation by means of dispersed systems such as emulsions, micelles, colloids, and polymer matrixes. It should be emphasized that all these processes involve the same fundamental aspects of mass and heat transfer phenomena between an SCF and a subcritical phase. Clearly the ultimate goal of all SCF particle technologies is to achieve predictable, consistent, and economical production of fine pharmaceuticals or chemicals. This is possible only on the basis of comprehensive mechanistic understanding and well-developed scale-up principles. 

Gygax, R., 1989, Explicit and implicit use of scale-up principles for the assessment of thermal runaway risks in the chemical production. Int Symp on Runaway Reactions, 52-73 (CCPS, AIChE. USA). 

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