Ethanol to Ethylene

Ethanol to Ethylene. The economics of this process depend on the availabiUty and price of ethanol. High volume production of ethylene... 

As described in Section 3.2.3, the use of acidic supports such as A1203 favors the dehydration of ethanol to ethylene, which leads to a severe carbon deposition.66,76,78,85 Reactions with lower H20/ethanol ratio can also favor several side reactions mentioned above and result in carbon deposition on the catalyst surface. Possible strategies to reduce the carbon deposition include (i) neutralization of acidic sites responsible for ethanol dehydration to ethylene and/or modification of the support nature, including less acidic oxides or redox oxides, (ii) use of a feed containing higher H20/ethanol molar ratio, and (iii) addition of a small concentration of air or 02 in the feed. 

Ethanol to ethylene process, 70 621 Ethanol transportation fuel, 70 60 Ethanol trifluoroborane, 4 144t Ethanol vapor concentration, effects in humans, 70 552t... 

The presence of oxygen enhances the catalyst stability. Breen et al. [187] investigated SRE over a range of oxide-supported metal catalysts. They concluded that the support plays an important role in the reaction. In fact, they observed that alumina-supported catalysts are very active at low temperatures for dehydration of ethanol to ethylene, which at higher temperatures (550 °C) is converted into H2, CO and CO2 as major products and CH4 as a minor product. The activities of the metal decrease in the order of Rh > Pd > Ni PS Pt. Ceria/zirconia-supported catalysts are more active and exhibit 100% conversion of ethanol at high space velocity and high temperature (650 °C). 

The reaction chemistry of simple organic molecules in supercritical (SC) water can be described by heterolytic (ionic) mechanisms when the ion product 1 of the SC water exceeds 10" and by homolytic (free radical) mechanisms when <<10 1 . For example, in SC water with Kw>10-11 ethanol undergoes rapid dehydration to ethylene in the presence of dilute Arrhenius acids, such as 0.01M sulfuric acid and 1.0M acetic acid. Similarly, 1,3 dioxolane undergoes very rapid and selective hydration in SC water, producing ethylene glycol and formaldehyde without catalysts. In SC methanol the decomposition of 1,3 dioxolane yields 2 methoxyethanol, il lustrating the role of the solvent medium in the heterolytic reaction mechanism. Under conditions where K klO"11 the dehydration of ethanol to ethylene is not catalyzed by Arrhenius acids. Instead, the decomposition products include a variety of hydrocarbons and carbon oxides. 

As mentioned earlier, at 500° C and 34.5 MPa supercritical water has a small dielectric constant, a very low ion product, and behaves as a high temperature gas. These properties would be expected to minimize the role of heterolysis in the dehydration chemistry. As shown in Table 1, the conversion of ethanol to ethylene at 500° C is small, even in the presence of 0.01M sulfuric acid catalyst. The appearance of the byproducts CO, C02) CH i+ and C2H6 points to the onset of nonselective, free radical reactions in the decomposition chemistry, as would be expected in the high temperature gas phase thermolysis of ethanol. 

The catalytic dehydration of ethanol to ethylene in SC water may be commercially important (16). Although high quality commercial alumina catalysts exist for the vapor phase dehydration of ethanol, the commercial processes require the ethanol feedstock to be relatively free of water. Hence the ethanol must be distilled from the ethanol-water mixture which is the product of fermentation processes. By avoiding this distillation step, and securing phase separation of the ethylene product from the ethanol-water reactant, SC dehydration of ethanol could enjoy advantages over existing commercial technologies. 

Tsao. U, Railly, J. W, Dehydrate ethanol to ethylene , Hydrocvbon Processing, 57 (2) 1 136 (1978). Farha, F. E, Banks, R. L, Triolefin process Chemistry and applications Petrochemical fotm-Americai Cor ressy Canqun, Mexico (12/18 Nov. 1978). 

Figure 10.8 Free energy change for ethanol to ethylene and water...

In the laboratory, P4O10 often finds use as a powerful dehydrating agent so powerful in fact that it can convert ethanol to ethylene, H2SO4 to SO3, HNO3 to N2O5, and... 

Ethanol is usually made most economically from ethylene, and not vice versa however, recent high natural gas prices and interest in ethanol from crops as a renewable raw material have prompted interest in the reverse process. U.S. 4,134,926 (to Lummus) describes a process for converting ethanol to ethylene with high yield. 

The conversion of ethanol is carried out in the presence of gas-phase oxygen molecules - oxidative dehydrogenation [47,48] - and the oxygen vacancies created in step 3a of Scheme 7.1 are regenerated by gas-phase oxygen. The dehydration of ethanol to ethylene and water does not consume surface oxygen atoms (step 3b). 

Removal of one or more molecules of H20 from a chemical compound, e.g., of ethanol to ethylene. 

The search continues for better and more economical processes for the production of ethylene. Those processes include catalytic thermal cracking, methanol to ethylene, oxidative coupling of methane, advanced cracking technology, adiabatic cracking reactor, fluidized bed cracking, membrane reactor, oxydehy-drogenation, ethanol to ethylene, propylene disproportionation, and coal to ethylene. Much work is still needed before any such process can compete with current processes. 

An example would be the dehydration of ethanol to ethylene and its dehydrogenation to acetaldehyde. If both reactions are first order, selectivity is unaffected by internal mass transport the ratio of the rates of reactions, 1 and 2 is k jkj at any position within the pellet. Equation (11-89) cannot be applied separately to the two reactions because of the common reactant A. The development of the effectiveness-factor function would require writing a differential equation analogous to Eq. (11-45) for the total consumption of A by both reactions. Hence k in Eq. (11-89) would be k- + k2 and Fp would be (Tp) -1- (rp)2- Such a development would shed no light on selectivity. 

The activity of alumina as a catalyst for alcohol dehydration varies considerably with the method of production of the active material. With hydrated alumina on pumice, ground, screened, and heated at 300° Goris20 concluded tliat the aldehyde reaction was predominant up to 450° C., below which the ethylene reaction was relatively unimportant but increased rapidly at higher temperature. Several other workers have failed to obtain appreciable decomposition of ethanol to ethylene over alumina at temperatures below 270° C.30 In contrast to this, Moser obtained yields of 50 to 60 per cent of ethylene over alumina at 250° to 300° C.31 Other... 

The equilibrium values for the dehydration of ethanol to ethylene have been calculated by Francis 08 and show that ethanol has a considerable tendency to decompose into ethylene. 

The experiments of Wibaut and Diekmann were perhaps the earliest to indicate the reversibility of the dehydration of ethanol to ethylene and water vapor. These workers found that when a mixture of water vapor and ethylene was passed over aluminum oxide or sulfate at 300° to 400° C., the reaction product contained 0.2 to 0.4 per cent of acetaldehyde. This was not the result of oxidation of ethylene as was shown by passing ethylene and air over the same catalysts at 360° C. From this they concluded that hydrolysis to alcohol had taken place as the primary reaction and that secondary dehydrogenation had formed acetaldehyde. 

The stop-effect, a drastic increase of the reaction rate when the feed concentration of a reactant is switched to zero, was studied for the dehydration of ethanol to ethylene on 7-alumina at 180 and 200°C. Two basic models exist in the literature to describe this phenomenon. They were discriminated on the basis of transient and periodic experiments, coupled with FTIR data of the adsorbed species. The model that best describes these measurements postulates the adsorption of ethanol on two different sites, S and S2, with a free S2 site being necessary for ethylene formation. 

Ethanol-to-ethylene oxide/ethylene glycols Ethylene oxide... 

Dehydration of ethanol to ethylene and gasoline (ETG) H-ZSM-5 Ethanol can be selectively transformed into diethylether (diesel fuel), ethylene, and hydrocarbons over H-ZSM-5 depending on reaction temperature [61]... 

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