Classical Process Synthesis

Process synthesis is a task of formulating the process configuration for a purpose by defining which operations or equipment are used and how they are connected together. There are two basic approaches for process synthesis 1) classical process synthesis, analysis and evaluation, and 2) optimization of process structure by using a suitable objective function. 

Classical process synthesis consists of the synthesis of the alternatives, their analysis and final evaluation. Hurme and Jarvelainen (1995) have presented a combined process synthesis and simulation system consisting of an interactive rule-based system which is used for generating process alternatives (Fig. 10). The process alternatives are simulated, costed and evaluated through profitability analysis. The developed system concept combines process synthesis, simulation and costing with uncertainty estimation. 

Conventionally, central and special metabolic pathways are distinguished. Central pathways are common to the decomposition and synthesis of major macromolecules. Actually, they are much alike in all representatives of the living world. Special cycles are characteristic of the synthesis and decomposition of individual monomers, macromolecules, cofactors, etc. Special cycles are extremely diversified, especially in the plant kingdom. For this reason, the plant metabolism is conventionally classified into primary and secondary metabolisms. The primary metabolism includes the classical processes of synthesis and deeradation of major macromolecules (proteins, carbohydrates, lipids, nucleic acids, etc.), while the secondary metabolism ensuing from the primary one includes the conversions of special biomolecules (for example, alkaloids, terpenes, etc.) that perform regulatory or other functions, or simply are metabolic end byproducts. 

Braun A variation on the classic ammonia synthesis process in which the synthesis gas is purified cryogenically. Widely used since the mid 1960s. 

These compounds can be prepared by using either classical processes for synthesis of amino acids (starting from the ad hoc precursor bearing fluorine on the aromatic moiety) or electrophilic fluorination of the arene moiety (e.g., elemental fluorine, xenon fluoride, acetyl hypofluorite). Although these methods are often poorly regioselective, they are useful for the preparation of F labeled molecules used in PET, for example, F tyrosine and dihydrophenylalanine (L-Dopa). ... 

The successful results and the green credentials of the process (water as cosolvent and only the nontoxic titanium dioxide as final residue) make this reaction an excellent, cheaper, and favorable alternative to the classical Strecker synthesis, which also requires the hydrolysis of cyanide to the amido group (Scheme 14.8c). 

Spontaneous asymmetric synthesis has been envisaged by theoretical models for more than 50 years [1-7]. This process features the generation and amplification of optical activity during the course of a chemical reaction. It stands in contrast to asymmetric procedures, such as stoichiometric resolution, conglomerate crystallization, or chiral chromatography, in which the optical activity can be increased but no additional chiral product is formed [8]. It is also different from classical asymmetric synthesis, in which new chiral product is obtained but the resulting enantiomeric excess (ee) is usually less than or, at most, equal to that of the chiral initiator or catalyst1. 

The addition of an allylic group was reported in the synthesis of heneicos-6-en-ll-one, the sex pheromone of the Douglas fir tussock moth.67 This method was compared advantageously to the classical processes employing the toxic tin hydrides, with respect to the rates, yields, and chemoselectivity.68,69 Concerning the stereoselectivity however, no major difference exists between the conventional and sonochemical methods.70,71... 

This case study deals with the design and simulation of a medium size plant of lOOkton cumene per year. The goal is performing the design by two essentially different methods. The first one is a classical approach, which handles the process synthesis and energy saving with distinct reaction and separation sections. In the second alternative a more innovative technology is applied based on reactive distillation. 

For the major part, ammonia production in the next 15 to 20 years will rely on the classic ammonia synthesis reaction combining nitrogen and hydrogen using a catalyst at elevated temperature and pressure in a recycle process. 

The Bohlmann-Rahtz reaction is a classic pyridine synthesis that has been studied and modified in many ways. Bagley et al. has elaborated on his previous work and reported an iodine-mediated catalytic Bohlmann-Rahtz reaction of aminodienone intermediates <05SL649>. This modified process is reported to be rapid at ambient temperatures resulting in good yields. Moreover, Bagley and co-workers presented a one-pot, three-component Bohhnann-Rahtz reaction to synthesize 2,3,6-trisubstituted and 2,3,4,6-tetrasubstituted pyridines 8 and 9 from P-ketoesters 10 and alkynes 11 as shown in Seheme 3 <05JOC1389>. 

Whereas biocatalysis previously was a last option that was only looked into when all other synthetic methods had failed, it is now a discipline well integrated into classical organic synthesis in the pharma-, agro-, and fine chemical industries [2]. An example from the latter group is laboratory chemicals producer Fluka, which has reported over 100 biocatalytic processes in routine production [3]. Biocatalysis can offer outstanding chemo-, regio- and/or enantioselectivities under mild reaction conditions. It is, hence, often used to create chirality, for example, in the pharma industry [4]. 

In the synthesis of phenylacetic acid, the Pd-TPPTS system was used as a catalyst by Kohlpaintner and Beller (Hoechst) [15] in a biphasic carbonylation of benzyl chloride as a greener alternative to the classical process the reaction of benzyl chloride with sodium cyanide (Equations 4.4 and 4.5). Although in the new process 1 equiv. of sodium chloride is formed, this is far less salt waste than in the original process. Moreover, sodium cyanide is about seven times more expensive per kilogram than carbon monoxide. 

Biocatalytic approaches in polymer synthesis have to include an optimized combination of biotechnological with classical processes. Therefore, this book starts with a thorough review on the sustainable, green synthesis of monomeric materials (Chapter 1). While few of the monomers presented in this chapter have been used in enzymatic polymerizations so far, the examples given could provide inspiration to use sustainable monomers more often in the future for enzymatic polymerizations and also for classical approaches. 

According to a recent conference given by Prof. Kita [162], the classical synthesis method currently used by Mitsui allows to produce about 250 zeolite membranes per day. Both the LTA and T types (Na K) membranes are now commercial and more than 80 pervaporation and vapor permeation plants are operating in Japan for the dehydration of organic liquids [163]. A typical pervaporation system, similar to the one described in [8], is shown in Fig. 11. One of the most recent applications concerns the production of fuel ethanol from cellulosic biomass by a vapour permeation/ pervaporation combined process. The required heat is only 1 200 kcal per liter of product, i.e. half of that of the classical process. Mitsui has recently installed a bio-ethanol pilot plant based on tubular LTA membranes in Brazil (3 000 liters/day) and a plant with 30 000 liters/day has been erected in India. The operating temperature is 130 °C, the feed is 93 % ethanol, the permeate is water and the membrane selectivity is 10 000. 

---