Scale-up and Reproducibility

Although hollow fibers are thought to be an excellent candidate to be used as support-they are cheap and have a very high surface area to volume ( 1000 m m ) - very few reports on hollow-fiber-supported zeolite membranes exist in the open literature. For zeohte membranes, ceramic hollow fibers are preferred because of their mechanical and thermal stability. Recently, Alshebani 

An important driver for zeolite membrane apphcations has been the commercialization of the NaA membranes for dehydration. However, for these membranes, the quality required is not as high as compared to gas-phase molecular sieving 

The reproducibility of zeolite membranes is sometimes questioned. But, taking into account the large surface areas that are produced for the mentioned application examples, for well-studied zeolite membrane syntheses this does not appear to be a limiting factor. 

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The amount of discodermolide produced would equate to around 3000 kg of sponge, a quantity that probably does not exist The total number of steps is 36 with an overall yield of 0.2% (main chain). This is on the low side, but it should be remembered that the yields for each step have not been optimized. The description of the various optimization processes in this article have only related to the various scale-up and reproducibility issues, not to obtaining the maximum possible yield, so there is plenty of scope for increasing the yield. There were, in this second campaign, some 18 chromatographic purifications. This has now been somewhat reduced to 14. The number of crystalline intermediates stands currently at 7. 

In plant cell cultures, shake flask culture is an indispensable stage of cultivation. Investigations in a shake flask are very essential and critical to bioprocess scale-up and optimization. We have developed a simple and convenient technique based on the principle of the Warburg manometric method to measure 02 uptake rate (OUR) and C02 evolution rate (CER) of suspended cells in a shake flask culture. This technique has been successfully applied to suspension cultures of Panax notoginseng cells, and some important bioprocess parameters, such as OUR, CER, respiratory quotient (RQ), SOUR and specific CER (SCER), were quantitatively obtained [99]. As long as the environment temperature is strictly controlled to within an error of 0.1 °C, the measuring system is accurate and reproducible, is easy to operate, is economical, and is also able to treat many samples simultaneously. 

A pure phenomenological model of such an intricate process, taking into account all possible reaction steps, is therefore a powerful tool for the scale up and the prediction of performances of trickle-bed reactors. Such a model (20 has proved to be able to correctly reproduce experimental data using only two adjustable parameters. It has been checked in several cases (hydrogenation of alphamethylstyrene (3J, hydrogenation of 2-butanone (, hydrorefining (J5) ), with more or less volatile liquid reactants and it appeared to be also useful to calculate a posteriori the extent of the different types of wetted catalyst area and their different effectiveness factor. 

Nevertheless, the development of zeolite-membrane reactors still requires improvements in the fluxes and separation factors attained to date, an objective to which many efforts have been devoted in recent years with the aim of materializing an industrial application of zeolite-membrane reactors. Several reviews have been published in the last 5 years dealing completely or partially with zeolite membranes [2,3,5,161,162,165-167]. Particularly, noteworthy have been the advances regarding the use of supports of different natures and characteristics (see Section 10.6.4), the control of the orientation and thickness of zeolite layers (see Section 10.2.1.2), and the preparation of new zeolite materials such as membranes (see Section 10.3). In spite of these advances, before zeolite-membrane reactors are used in industry (see Section 10.6.5), signihcant progress must be achieved in more prosaic issues such as scale-up and control of the synthesis process to increase membrane reproducibility. 

Establishing a reproducible process in place, scaling up, and developing the respective specifications. 

SPD techniques like ECAP share several advantages including high potential for scaling up, high reproducibility, and notable effectiveness in producing nanostructured bulk materials from ductile metals and alloys of initially low to moderate strengths. 

A very important aspect, which should be dealt with in the design of new - and the discussion of the known - protocols, is the stability or, more correctly, the robustness of the catalytic process itself. By this, we mean the dependence of a running process on the deviation of parameters The more robust or deviation-proof a given process is, the more convenient it is in synthetic terms to be reproduced, scaled-up and extended in scope. The type 1 systems are the most robust. In fact, these processes might be regarded as the... 

Owing to its direct impact on the performance and efficiency of the process, feed rate is an important factor to consider during development. Representative feed rates that can be geometrically scaled up ensure reproducibility of the process and product. Multiple feeders can be used to improve the throughput as long as the product robustness has been established in that feed rate range. 

Although fluidized sand or alumina can also be used in the jacket of these somewhat larger reactors, the size makes the jacket design a problem in itself, hence these reactors are seldom used. An advantage of the jacketed reactor is that several—usually four—parallel tubes can be placed in the same jacket. These must be operated at the same temperature, but otherwise all four tubes can have different conditions if needed. This type of arrangement saves time and space in long-lasting catalyst life studies. Jacketed tubular reactors come close, but still cannot reproduce industrial conditions as needed for reliable scale-up. Thermosiphon reactors can be used on all but the most exothermic and fast reactions. 

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