Ethanol and Higher Alcohols

Carbonylation activity of ethanol using ethyl iodide as a promoter has been investigated using RhNaX as a catalyst (208,211). Some carbonylation activity does occur, with formation of ethyl propionate however, ether and also olefin formation results in rather poor selectivities to the ester. The selectivity decreases with increasing ethanol conversion. Olefin formation was ascribed to a dehydrohalogenation reaction, i.e., 

The observed lack of an overall consumption of ethyl iodide was attributed to reaction of HI with ethanol (211), i.e., 

A comparison of the absolute rates of methanol and ethanol carbonylation (211) indicated that the poor selectivity in the latter case is due to an increase in the rates of the side reactions rather than a large decrease in the rate of carbonylation. These results contrast with the homogeneous system, where ethanol carbonylation was reported (218) to be considerably slower (18 times) than with methanol. 

Nefedov et al. (219) found that Fe203 impregnated on RhNaX had a promoting effect on ethanol carbonylation selectivity as was the case for methanol (215). 

Christensen et al. (208) were unable to carbonylate 2-propanol using RhNaX, but few details were given. Russian workers (220), however, showed that the carbonylation rate of higher alcohols could be markedly increased over RhNaX, by increasing the CO pressure. 

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Formation of esters using ethanol and higher alcohols. Mix 1 cm3 of ethanol and 1 cm3 of glacial ethanoic acid. Add 2 drops of concentrated sulfuric acid and warm the mixture for a few minutes. Then pour the mixture into a beaker of cold water. The distinctive smell of an ester can be detected. Repeat the procedure using higher alcohols - propanol, butanol and pentanol. 

In the case of ethanol and higher alcohols the zeolite matrix may well have a negative effect in that it might favor dehydration or dehydrogenation reactions to form ethers and olefins. 

It is often found to be more difficult to produce esters of ethanol and higher alcohols than methanol. Dreger (66) overcame this inefficiency in forming esters by using two-stage trani-esterification and two alcohols, one of which is methanol. The reaction produced a mixed ester, but the yield was significantly improved. 

The fuel grade methanol is 98% pure and contains such impurities as water, ethanol and higher alcohols. The impurities would have to be removed by distillation to produce chemical grade methanol of 99.90% purity containing ethanol and water contents of no more than 900 ppm and 500 ppm respectively (7). It is estimated for the present study that an additional 2% thermal efficiency is lost for the distillation operation. 

Ethanol and Higher Alcohols from Syngas. Direct synthesis of ethanol from syngas is intensely investigated especially in North America. Another approach in this context is the homologjzation of methanol, i.e. the reaction of methanol with syngas to yield ethanol. Higher alcohols can also be formed. The reactions are summarized in equations (8.3) and (8.4). 

This section is devoted to a brief description of the main comptments of DAFC as an introduction to the most exhaustive analysis in Chaps. 2, 3,4, and 5 for electrocatalysts for methanol, ethanol, and higher alcohols, in Chap. 6 for proton exchange and alkaline membranes, and Chap. 7 for carbonous materials used as catalysts support, gas diffusion layers and bipolar plates. 

The permeability of ethanol and higher alcohols through Nafion has not been studied so extensively as methanol permeation. Verma and coworkers reported the permeability coefficients of ethanol through Nafion composites with NdaOa [90], neodymium triflate [91], and erbium triflate [92] and the corresponding Nafion recast membranes. Unexpectedly, the measured P for ethanol differ more than a factor 20 for recast membranes (P between 1.0 10 and 2.8.10 cm. s ). 

Alcoholic OTW The general effect of ethanol and higher alcohols. Ethanol, 50 g/1... 

Furthermore, poor results are obtained for the solubilities and activity coefficients at infinite dilution of alkanes or naphthenes in water. This was accepted by the developers of modified UNIFAC to achieve reliable VLE results, for example, for alcohol/water systems. The reason was that starting from experimental g -values of approx. 250000 for n-hexane in water at room temperature it was not possible to fit alcohol-water parameters which deliver y -values for hexanol in water of 800 and at the same time describe the azeotropic composition of ethanol and higher alcohols with water properly and obtain homogeneous behavior for alcohol-water systems up to C3-alcohols and heterogeneous behavior starting from C4-alcohols. To allow for a prediction of hydrocarbon solubilities in water an empirical relation was developed [61, 62], which allows the estimation of the solubilities of hydrocarbons in water and of water in hydrocarbons (see below). 

If DAFCs fuelled with ethanol and higher alcohols have a commercial future, this seems to be indissolubly linked to Pd-based electrocatalysts and anion-exchange membranes. As shown in this Chapter, the known catalytic architectures for alcohol oxidation are extremely valid, yet they suffer the scarce ability to cleave C-C bond in a selective way as well as poisoning by COads. Therefore increasing research efforts are required to design new catalysts with better performance and higher electrochemical stability. 

Direct Synthesis of Ethanol and Higher Alcohols from CO/H2... 

Clearly, the slate of chemicals produced from coal-derived synthesis gas will expand as new technologies are developed, and supplies of petroleum and natural gas dwindle. The most likely such chemicals are those for which existing processes have been demonstrated but which presently lack economic merit. Relatively small improvements in technology, shifts in feedstock availability, capital costs, or political factors could enhance the viability of coal-based processes for the production of methanol, ethanol, and higher alcohols, vinyl acetate, ethylene glycol, carboxylic acids, and light olefins. 

Glorius and co-workers reported an alternative approach for the synthesis of formamides by dehydrogenative coupling of methanol with amines. The dehydrogenation of methanol is energetically disfavoured AH=84 kJmol ) compared to ethanol and higher alcohols [AH = 68 kj moP ) and few reports of couplings with methanol exist presumably for this reason. ... 

On the other hand, methanol is rather toxic, so why not use ethanol, which is less toxic, has similar physical properties (m.p. -114.3 °C b.p. +78,4 C density 0.789 gm cm ) and is also inexpensive It turns out that ethanol and higher alcohols cannot be oxidized all the way to CO2, at least not at the potentials relevant to fuel cell operation. The product of electrochemical oxidation is acetic acid in the case of ethanol and the corresponding higher acid in the case of higher alcohols. It seems that breaking the C-H and the 0-H bonds in methanol is easier that breaking the C-C bond in ethanol. 

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