Ethanol formation

Its appeal Hes in the fact that synthesis gas can be produced from trash, municipal sewage, scrap wood, sawdust, newsprint, or other waste. The early work of Fischer and Tropsch on methanol synthesis showed that ethanol could be obtained in the process (165) and that by certain modifications the proportion of ethanol in the product could be increased (166). The Hterature concerning this method is extensive (167—176). The conditions that favor ethanol formation are 125—175°C and 1.42 MPa (14 atm) in the presence of reduction catalysts such as powdered iron. 

The catalytic alcohol racemization with diruthenium catalyst 1 is based on the reversible transfer hydrogenation mechanism. Meanwhile, the problem of ketone formation in the DKR of secondary alcohols with 1 was identified due to the liberation of molecular hydrogen. Then, we envisioned a novel asymmetric reductive acetylation of ketones to circumvent the problem of ketone formation (Scheme 6). A key factor of this process was the selection of hydrogen donors compatible with the DKR conditions. 2,6-Dimethyl-4-heptanol, which cannot be acylated by lipases, was chosen as a proper hydrogen donor. Asymmetric reductive acetylation of ketones was also possible under 1 atm hydrogen in ethyl acetate, which acted as acyl donor and solvent. Ethanol formation from ethyl acetate did not cause critical problem, and various ketones were successfully transformed into the corresponding chiral acetates (Table 17). However, reaction time (96 h) was unsatisfactory. 

Ethanol can be derived from biomass by means of acidic/enzymatic hydrolysis or also by thermochemical conversion and subsequent enzymatic ethanol formation. Likewise for methanol, hydrogen can be produced from ethanol with the ease of storage/transportation and an additional advantage of its nontoxicity. Apart from thermodynamic studies on hydrogen from ethanol steam reforming,117-119 catalytic reaction studies were also performed on this reaction using Ni-Cu-Cr catalysts,120 Ni-Cu-K alumina-supported catalysts,121 Cu-Zn alumina-supported catalysts,122,123 Ca-Zn alumina-supported catalysts,122 and Ni-Cu silica-supported catalysts.123... 

Alcohol recovery from the fermentation brews was less than complete in most cases, which may be attributable to less than ideal conditions. The best yields, 60 to 97% of theory, were obtained with sugars obtained by hydrolysis of cellulosic residues of the autohydrolysis-extraction process. Unextracted pulps, or the hemicellulose solutions, gave poor ethanol formation, which suggests inhibition. In the calculation of material and energy balances which follows, we have assumed 95% yields of ethanol from wood sugars, which is readily achieved in industrial practice and which we believe to be achievable with our wood sugars as well. 

The mixture composition depends strongly on the Et0H H20 ratio, while the highest yields of pyran have been achieved in absolutized ethanol. Formation of 6-ethoxydihydropyran 53 possibly can be attributed to the influence of the CF3 group, which is a very strong acceptor and its presence in carbonyl compounds promotes acetal formation. 

The possibility of ethanol formation by such a reaction pathway was tested by different probe molecule experiments. As can be seen in figure 3 the introduction of acetaldehyde in the CO+H flow on a Rh/CeO catalyst enhanced the ethanol formation. The same experiment with Rh/SiO left all the other products including ethanol unchanged. These result are in agreement with those observed recently by Bell... 

Sanchez LB (1998) Aldehyde dehydrogenase (CoA-acetylating) and the mechanism of ethanol formation in the amitochondriate protist, Giardia lamblia. Arch Biochem Bio-phys 354 57-64... 

Dry ethanol and concentrated sulfuric acid Silver nitrate Evolves ethyl acetate (fruity odor) upon heating dry isoamyl alcohol may be substituted for ethanol Formation of white precipitate of silver acetate that is soluble in dilute ammonia solution... 

This mechanism is highly attractive owing to the simplicity of the Fe3+ O OC Hs complex formation and its conversion to reaction products with an eliminated stage of fixed ethanol formation by means of intramolecular regrouping. 

Since 5 is symmetrical (it has a plane of symmetry and is achiral) it doesn t matter which carbonyl reacts so the sequence of symmetry breaking with ethanol, formation of the acid chloride 7 and reduction of the acid chloride gives the aldehyde 8 ready for the aldol step. 

The kinetic rates of growth, death, ethanol formation and substrate consumption are as follows ... 

Measuring the C02 evolution, CER, is an excellent way to monitor the ethanol production since the dominant source of C02 production in anaerobic fermentations is directly linked to ethanol formation (13). One of the main goals of the present project was to maximize ethanol production. The feed rate, F(t), which maximizes the overall ethanol production, 1(F) (Eq. 1), for a given time, t, should therefore be found (16) ... 

Sanchez LB (1998) Aldehyde dehydrogenase (CoA-acetylating) and the mechanism of ethanol formation in the amitochondriate protist, Giardia lamblia. Arch Biochem Biophys 354 57-64 Saraste M (1999) Oxidative phosphorylation at the fin de siecle. Science 283 1488-1493 Saruta F, Kuramochi T, Nakamura K, Takamiya S, Yu Y, Aoki T, Sekimizu K, Kojima S, Kita K (1995) Stage-specific isoforms of complex II (succinate-ubiquinone oxidoreductase) in mitochondria from the parasitic nematode, Ascaris suum. J Biol Chem 270 928-932 Scheffler I (1999) Mitochondria. Wiley-Liss, New York... 

It is clear that phosphate is required for the continued operation of glycolysis and ethanol formation. In extracts to which glucose is added, fermentation proceeds until ADP and P4 (present in the extracts) are exhausted. 

The outstandingly rapid principle of fluorescence measurements served excellently for the controlled suppression of ethanol formation during continuous baker s yeast production [280]. 

The yeast growth is diauxic 17). Under the conditions of glucose repression, ethanol formation takes place even in the presence of oxygen. Yeasts require a small but finite oxygen supply for synthesis of unsaturated fatty acids, sterols, and nicotinic acid. These compounds which are essential to membrane functions are synthesized only aerobically 18). 

Using the catalyst system known from the Monsanto process, Dumas et at. have been able to direct the reaction towards ethanol formation using syngas mixtures extremely rich in hydrogen [87]. As is shown in Table XII, no acetic acid and only minor amounts of acetates are formed at an H3/CO ratio of 60. Ethanol and acetaldehyde aie the main products along with considerable amounts of methyl ethyl ether. Unfortunately, the Dumas c/ at. based the yields and conversion on carbon monoxide and not on methanol. This makes the data of this interesting process difficult to compare with those of other catalyst systems. 

Deuteration experiments showed that the p-H atom in the product stems from borohydride whereas the a-H atom is introduced by proton transfer from ethanol. Formation of the a-(C-H) bond is nonstereoselective accordingly, the reduction of analogous substrates with an a- instead of a p-disubstituted double bond leads to racemic products (a mechanistic model rationalizing the stereoselectivity of (semicorrinato)cobalt catalysts is available ). 

Table 11.10 is a summary of the different conversion schemes and conditions for thermochemical ethanol formation discussed here. The primary routes to ethanol and ethanol precursors from synthesis gas are evident. It remains to be determined whether any of these technologies can be developed to produce low-cost thermochemical ethanol. 

Synthetic ethanol is now produced by hydration of ethylene. Ethanol is one of important chemicals. Though ethanol synthesis from H2/CO was extensively studied so far, there are a few reports about ethanol synthesis from H2/CO2. Recently, some efficient catalysts for ethanol formation from H2/CO2 were developed by Arakawa and his co-workers. 

Ethanol synthesis bv promoted Rh/ Si02 catalyst It is known that ethanol can be synthesized efficiently from H2/CO by promoted Rh/Si02 catalyst.[42.43] Based on this result, promoted Rh/Si02 catalysts were tested for C02 hydrogenation to ethanol. [44,45] As a result, it has proved that Sr, Li and Fe additives are effective for ethanol formation. [46,47] Typical results are shown in Table 4. [48] It is speculated reaction proceeds via equation(l) and (2). Acetyl species, formed by CO insertion to methyl species on Rh surface, is supposed to be a possible reaction intermediate. 

We have been studying the feasibility of CO2 hydrogenation to oxygenates over silica supported rhodium catalysts based on the results obtained through CO hydrogenation. In previous papers, we reported that the effect of additives to Rh/SiOz catalysts. As a result, we found that only four additives ( Li, Fe, Sr, and Ag ) showed ethanol formation [1-3]. 

It has been reported that the precursors of catalyst components over promoted Cu catalysts influence reaction behavior of CO2 hydrogenation. Nitta et al. has reported that the precursor components of the precipitated Cu-ZrOz catalysts have a great influence on the methanol selectivity as well as CO2 conversion [4]. Based on these findings through CO2 hydrogenation, it is considered that appropriate choice of the precursors in the preparation of supported metal catalyst might improve ethanol formation in CO2 hydrogenation. 

RhY (Li/Rh = 10). Simultaneously, promotion of not only methanol but also ethanol was observed. It is a peculiar phenomenon that production of ethanol was enhanced without methane formation though ethanol should be generated from surface methyl groups. We expected that gas phase CO which was produced during the reaction had some contribution to ethanol formation. So we mixed 1.8% of CO with H2H-C02... 

---