Scaling-down chemical processes

As mentioned before, scaling-down chemical processes and making them modular is an essential element for a new vision of sustainable industrial chemistry. 

Rotameters The rotameter, an example of which is shown in Fig. 10-21, has become one of the most popular flowmeters in the chemical-process industries. It consists essentially of a plummet, or float, which is free to move up or down in a vertical, slightly tapered tube having its small end down. The fluid enters the lower end of the tube and causes the float to rise until the annular area between the float and the wall of the tube is such that the pressure drop across this constriction is just sufficient to support the float. Typically, the tapered tube is of glass and carries etched upon it a nearly linear scale on which the position of the float may be visually noted as an indication of the flow. 

GEMEP uses conventional chemical processing equipment and can be easily and economically scaled up or down. 

A volume priced approach, either bottom-up or top-down, is used for fine chemicals produced on an industrial scale a time-based one is used for those produced on a small scale, or for process research. The most frequently used unit for the former is /kg, respectively FTE (full-time equivalent) for the latter. 

There are a number of alternatives and variations to the reduced mechanism method. The intrinsic low dimensional manifold (ILDM) approach [253] and similar methods [399] seek to decouple the fastest time scales in the chemistry. There is a wide range of time scales for chemical reactions in most high-temperature processes, from 10-9 second to seconds. Fast reactions, or reactions with small time scales, quickly bring composition points down to attracting manifolds in the composition space. Then composition points move along on manifolds. In the ILDM approach it is assumed that any movement of the... 

TMVs offer exciting perspectives for further chemical processing as they are not only monodisperse in size but also offer a well defined surface chemistry down to molecular scale. This has already been used by several groups for further chemical modification of TMVs like metallization and mineralization [86-92], In particular, metal wires could be created by controlled metallization of the viruses. This line of research is currently being pursued. 

Zufferey, B. and Stoessel, F. (2007) Safe scale up of chemical reactors using the scale down approach, in 12th International Symposium Loss Prevention and Safety Promotion in the Process Industries, IchemE, Edinburgh. 

Zuflerey, B. (2006) Scale-down Approach Chemical Process Optimisation Using Reaction Calorimetry for the Experimental Simulation of Industrial Reactors Dynamics, EPFL, n°3464, Lausanne. 

Hydrogen is present in fossil fuels and water in sufficient quantities that it can be produced on a large scale by three different methods 1) Petrochemical Processes, 2) Coal-based Chemical Processes and 3) Electrochemical Processes (Electrolysis). In Table 5.7, the percentage of hydrogen production is broken down by type of manufacturing process for the years between 1974 and 198846. A similar distribution for 2002 is shown in Table 5.8162. 

Once chemists have developed a product in a laboratory, it is up to chemical engineers to design a process to make the product in commercial quantities as efficiently as possible. "Scaling up" production is not just a matter of using larger beakers. Chemical engineers break down the chemical process into a series of smaller "unit operations" or processes and techniques. 

L-Tryptophan (L-Trp) was produced, mainly by Japanese companies, on a scale of 500-6001 a-1 in 1997 [70]. It is an essential amino acid that is used as a food and feed additive and in medical applications. L-Trp is, at US 50 kg-1 (feed quality), the most expensive aromatic amino acid and it is thought that the market for L-Trp could expand drastically if the production costs could be brought down. There is no chemical process for L-TrP and enzymatic procedures starting from indole, which were very efficient, could not compete with fermentation [95]. L-Trp has been produced by precursor fermentation of anthranilic acid (ANT, see Fig. 8.16), but the serious effects of minor by-products caused the process to be closed down. Since the mid-1990s all L-Trp is produced by de novo fermentation. 

We have discussed a series of examples and aspects, such as the problem of risk and sustainability assessment, tools and principles for a sustainable industrial development (in particular, the issue of scaling-down and intensification of chemical processes, and the role of catalysis), and problems and opportunities in substituting chemical and processes (also in the view of REACH legislation, and of the international chemicals policy on sustainability). These topics are expanded in the following chapters, while the final section on industrial case histories for sustainable chemical processes provides further hints on these aspects. 

The manufacture of pharmaceutical chemicals in some ways resembles a scaled-up version of the organic chemical syntheses carried out in the laboratory and, in others, a scaled down version of the processes used in the heavy chemicals industry. The heavy chemicals industry manufactures commodity chemicals that are largely undifferentiated and have to be sold at the ruling market price. The individual company, having little control over prices, is therefore preoccupied with reducing costs. A major source of cost reduction is economies of scale, and those in turn are related to the use of continuous rather than batch processes. The former are well-nigh universal in the heavy chemicals sector. 

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