Thermodynamic equilibria synthesis

In the original announcement of the workshop the participants were told that everything was to be taken from methanol synthesis except the kinetics. Some may have interpreted this to mean that the known thermodynamic equilibrium information of the methanol synthesis is not valid when taken together with the kinetics. This was not intended, but... 

When the reaction conditions approach the thermodynamic equilibrium, isomerization follows. The distribution of the double bond is statistical. The molecular formation in the disproportionation stage is also statistical. Normally a run will produce 10-15% by weight of product, which is then suitable for LAB synthesis after distillation. The physical data of these internal olefins are shown in Table 4 [41]. 

If the polyester synthesis is performed with equimolar amounts of diol and diacid, then, in addition to hydroxy, carboxy-terminated oligomers, dihydroxy- and dicarboxy-terminated oligomers are formed, as shown below. In a thermodynamic equilibrium, the molar ratios of the three functionality fractions should be 2 1 1, respectively. 

The ODH of ethylbenzene to styrene is a highly promising alternative to the industrial process of non-oxidative dehydrogenation (DH). The main advantages are lower reaction temperatures of only 300 500 °C and the absence of a thermodynamic equilibrium. Coke formation is effectively reduced by working in an oxidative atmosphere, thus the presence of excess steam, which is the most expensive factor in industrial styrene synthesis, can be avoided. However, this process is still not commercialized so far due to insufficient styrene yields on the cost of unwanted hydrocarbon combustion to CO and C02, as well as the formation of styrene oxide, which is difficult to remove from the raw product. 

The hydrocarbon feedstock is reacted with a mixture of oxygen or air and steam in a sub-stoichiometric flame. In the fixed catalyst bed the synthesis gas is further equilibrated. The composition of the product gas will be determined by the thermodynamic equilibrium at the exit pressure and temperature, which is determined through the adiabatic heat balance based on the composition and flows of the feed, steam and oxygen added to the reactor. The synthesis gas produced is completely soot-free [28]. 

Obviously, equation 8 suggests that the ideal synthesis gas reactor should operate at a CH4 02 mole ratio of 2 1 (29.6% CH4 in air) if total conversion of the reactants occurs. At high enough temperatures, this mixture is completely converted to H2 and CO at thermodynamic equilibrium. Below about 1270 K, the equilibrium mole fraction of carbon becomes significant. Hence, a reactor must be maintained above 1270 K to avoid carbon formation. 

Enzymatic synthesis in reaction mixtures with mainly undissolved substrates and/or products is a synthetic strategy in which the compounds are present mostly as pure solids [28, 29]. It retains the main advantages of conventional enzymatic synthesis such as high regio- and stereoselectivity, absence of racemization, and reduced side-chain protection. When product precipitates, the reaction yields are improved, so that the necessity to use organic solvents to shift the thermodynamic equilibrium toward synthesis is reduced and synthesis is made favorable even in water. 

Figure 12.2 Time courses of kinetically controlled and thermodynamically controlled synthesis. The dotted line represents the position of the thermodynamic equilibrium.

Positional Isomerization. A different type of isomerization, substituent migration, takes place when di- and polyalkylbenzenes (naphthalenes, etc.) are treated with acidic catalysts. Similar to the isomerization of alkanes, thermodynamic equilibria of neutral arylalkanes and the corresponding carbocations are different. This difference permits the synthesis of isomers in amounts exceeding thermodynamic equilibrium when appropriate reaction conditions (excess acid, fast hydride transfer) are applied. Most of these studies were carried out in connection with the alkylation of aromatic hydrocarbons, and further details are found in Section 5.1.4. 

Dr. Friedel. No. The Fischer-Tropsch synthesis is not an equilibrium process. Thermodynamic equilibrium would predict products with much more extensive branching than is found to occur at Fischer-Tropsch synthesis temperatures. 

On his initiative, A. G. Doroshkevich and I. D. Novikov [56] constructed a global spectrum of the electromagnetic radiation in the Universe and showed that relic radiation in thermodynamic equilibrium can be found in the centimeter region. The discovery of relic radiation answered the question of what model to choose for the Universe. Ya.B. became an ardent proponent of the theory of a hot Universe (see the 1966 review [26 ]). He was one of the first in the world to understand what a powerful tool relic radiation represented for discovery of the Universe s past. His reviews of 1962-1966, which became the basis for excellent books written later with I. D. Novikov [57-59], contain practically all the ideas which have now become the methods for studying the large-scale structure of the Universe. These include the question of dipole and quadrupole anisotropy, and of angular fluctuations of relic radiation, the problem of nuclear synthesis reactions in the hot Universe, and the quark problem, first raised by Ya.B. together with L. B. Okun and S. B. Pikelner (1965) [11 ]. 

Such complexes form a precursor to a full discussion of the vast and highly topical field of self-assembly (Chapter 10). We consider them here since they resemble structurally the types of compounds discussed in Section 4.7, but unlike metal-based anion receptors the simple thermodynamic equilibrium between host, anion and complex is not the only process occurring in solution. In fact multiple equilibria are occurring covering all possible combinations of interaction between anions, cations and ligands. These systems have the appeal that the formation of particular metal coordination complexes are thus subject to thermodynamic anion templating (cf. the thermodynamic template effect in macrocycle synthesis, Section 3.9.1) and vice versa. 

The calculated thermodynamic equilibrium conversions and product compositions for propylene disproportionation at 200 to 400 C were reported by Heckelsberg, Banks, and Bailey16). Atlar, Pis man, and Bakhshi-Zade 8S) made similar calculations for the 50 - 300 °C range. They noted that the equilibrium constants were independent of pressure. Banks and Regier 57) showed thermodynamic equilibrium conversions as a function of temperature for the various reactions involved in the synthesis of isoamylene via disproportionation (Fig. 3). A comparison of calculated equilibrium composition for... 

Metabolism cannot occur in a system that is at thermodynamic equilibrium. The synthesis of molecules and the construction of cellular structures require energy that an organism must obtain from the environment and that... 

Solid materials, even at elevated temperatures, may not often achieve thermodynamic equilibrium due to the slowness of mass transport in solid state. Metastable equilibria (well known for glasses) may then be established. This makes it possible to prepare metastable solid solutions in wider compositional ranges if compared to thermodynamic equilibrium, by using various synthesis techniques at relatively low temperatures. 

The thermodynamic equilibrium is most favourable at high pressure and low temperature. The methanol synthesis process was developed at the same time as NH3 synthesis. In the development of a commercial process for NH3 synthesis it was observed that, depending on the catalyst and reaction conditions, oxygenated products were formed as well. Compared with ammonia synthesis, catalyst development for methanol synthesis was more difficult because selectivity is crucial besides activity. In the CO hydrogenation other products can be formed, such as higher alcohols and hydrocarbons that are thermodynamically favoured. Figure 2.19 illustrates this. 

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