Ethene supercritical

Alcohols undergo dehydration in supercritical and hot water (41). Tertiary alcohols require no catalyst, but secondary and primary alcohols require an acid catalyst. With 0.01 MH2SO4 as a catalyst, ethanol eliminates water at 385°C and 34.5 MPa to form ethene. Reaction occurs in tens of seconds. Only a small amount of diethyl ether forms as a side reaction. 

One example will show the manifold types of reactions studied by Mok et al. (1989). Lactic acid decomposes in supercritical water to give acetaldehyde, which then reacts further it can also undergo dehydration to give acrylic acid, which is either hydrogenated to give propionic acid or decarboxylated to give ethene (Fig. 7.4). 

SCFs will find applications in high cost areas such as fine chemical production. Having said that, marketing can also be an issue. For example, whilst decaffeina-tion of coffee with dichloromethane is possible, the use of scCC>2 can be said to be natural Industrial applications of SCFs have been around for a long time. Decaffeination of coffee is perhaps the use that is best known [16], but of course the Born-Haber process for ammonia synthesis operates under supercritical conditions as does low density polyethylene (LDPE) synthesis which is carried out in supercritical ethene [17]. 

Figure 10.16 illustrates the solubility of naphthalene in supercritical ethene as a function of temperature at different pressures. In Fig. 10.16 the temperature dependence of solubility is different in different pressure areas. At high pressure, an increase in temperature is followed by an increase in solubility, whereas at lower pressures the opposite effect occurs. 

Fig. 10.16 Solubility of naphthalene in supercritical ethene as function of temperature at different pressures. 

Early work (7) in this laboratory established the heterolytic nature of ethanol dehydration in supercritical water. Trace (0.001 to 0.01 M) concentrations of strong mineral acids (such as H2SO4 and HCl) were found to catalyze significant conversions of ethanol to ethene in water at 385 C, 34.5 MPa after a few... 

Brennecke et al. have described an important study of exciplex and excimer formation in supercritical carbon dioxide and ethene. 

Supercritical or near-critical fluids can be used both for extraction and chromatography. Many chemicals, primarily organic species, can be separated and analyzed using this approach [6], which is particularly useful in the food industry. Substances that are useful as supercritical fluids include carbon dioxide, water, ethane, ethene, propane, xenon, ammonia, nitrous oxide, and a fluoroform. Carbon dioxide is most commonly used, typically at a pressure near 100 bar. The required operating pressure ranges from about 43 bar for propane to 221 bar for water. Sometimes a solvent modifier is added (also called an entrainer or cosolvent), particularly when carbon dioxide is used. 

Other biphasic C—C bonding reactions were carried out with fluorous solvents, for instance Suzuki- and Sonogashira-couplings [124] or ethene or propene oligomerizations [125, 126], Further new solvent systems use ionic liquids for the linear dimerisation of 1-butene to octenes [127] or the hydrovinylation of styrene with a combination ionic liquid/supercritical carbon dioxide [128] (cf. Section 7.4). 

In the following sections some aspects of (potential) applications of sc-fluids in the fine chemical industry with respect to product separation/purification and catalytic reactions are discussed. Earlier industrial applications of supercritical fluid reactions, for example the Haber-Bosch process for the synthesis of ammonia, synthesis of methanol from hydrogen and carbon monoxide, or the polymerization of ethene will not be discussed. An extensive overview on the use of sc-fluids in the synthesis of bulk chemicals is given in the book edited by fessop and Leitner [12],... 

Figure 3.1-7 A series of FTIR spectra obtained from a modified ATR-FTIR probe inserted into a high pressure autoclave. The spectra were collected over a period of 40 min and show the depletion of acrylic acid monomer in a concentrated (30% by volume) SCCO2 solution at 70 °C and 180 bar in the presence of AIBN initiator. The bands observed correspond well with those observed previously for acrylic acid in supercritical ethene [64].

This chapter focuses on recent advances in high-pressure ethene homo- and copolymerization that have emerged from applying pulsed-laser-assisted techniques to the measurement of rate parameters, from using on-line spectroscopic monitoring of polymerization Under extreme supercritical conditions, and from introducing simulation tools into data analysis. 

As shown in Scheme 4.7-10, the RCM process differs remarkably from all previously discussed reactions in SCCO2 in that a gaseous compound, ethene, is produced in this reaction, rather than consumed as in the other examples. At first sight, it seems unreasonable to carry out such a reaction under high pressure, but the equilibrium of the reversible RCM process is of course only influenced by the partial pressure of the components, whereas the total pressure is mainly due to the supercritical solvent. There is, however, a remarkable influence of the total pressure on the selectivity of the metathesis reaction the RCM product is obtained in high yields at high pressure, whereas mainly... 

---