Synthesis, of methanol

Methanol (qv) is one of the 10 largest volume organic chemicals produced in the wodd, with over 18 x 10 t of production in 1990. The reactions for the synthesis of methanol from CO, CO2, and H2 are shown below. The water gas shift reaction also is important in methanol synthesis. 

Commercial isobutyl alcohol is made almost exclusively from the hydrogenation of isobutyraldehyde obtained by the hydroformylation of propylene. However, this alcohol is also commonly obtained as a coproduct in the Eischer Tropsch synthesis of methanol (16,17). 

When a reaction has many participants, which may be the case even of apparently simple processes like pyrolysis of ethane or synthesis of methanol, a factorial or other experimental design can be made and the data subjected to a re.spon.se. suiface analysis (Davies, Design and Analysis of Industrial Experiments, Oliver Boyd, 1954). A quadratic of this type for the variables X, Xo, and X3 is... 

A tubular reactor is to be designed for the synthesis of methanol from a stoichiometric mixture of CO and Hj. The reaction occurs in the vapor phase using a solid catalyst in the form of porous spheres CO + 2H2 = CH3OH. The average mixture physical and thermodynamic data at 500 K and 10 Mpa are... 

This example illustrates one of the ways in which the catalyst chemist must study and use the work of others it illustrates the importance of constraints not involving the catalyst directly. Other cases can be found where the catalyst performance has a more direct bearing on the easing of constraints. The synthesis of methanol provides such an example ... 

The process begins with a gasification process that converts coal into carbon monoxide and hydrogen. Part of this gas is sent to a water-gas shift reactor to increase its hydrogen content. The purified syngas is then cryogenically separated into a carbon monoxide feed for the acetic anhydride plant and a hydrogen-rich stream for the synthesis of methanol. 

This is illustrated by the TPD spectra of formate adsorbed on Cu(lOO). To prove that formate is a reaction intermediate in the synthesis of methanol from CO2 and H2, a Cu(lOO) surface was subjected to methanol synthesis conditions and the TPD spectra recorded (lower traces of Fig. 7.13). For comparison, the upper traces represent the decomposition of formate obtained by dosing formic acid on the surface. As both CO2 and H2 desorb at significantly lower temperatures than those of the peaks in Fig. 7.13, the measurements represent decomposition-limited desorptions. Hence, the fact that both decomposition profiles are identical is strong evidence that formate is present under methanol synthesis conditions. 

Table 8.3. Mole fractions of CO, H2 and CH3OH in the direct synthesis of methanol.

Recent research on the catalytic synthesis of methanol from CO2 and H2 over a copper catalyst has shown that the rate of reaction is first order in CO2 and 3/2 in H2. 

From a prachcal standpoint, formic acid or its salts are the least valuable reaction products. The energy content of formic acid upon its reverse oxidation to CO2 is insignificant, and its separation from the solutions is a labor-consuming process. At present, maximum effort goes into the search for conditions that would ensure purposeful (with high faradaic yields) synthesis of methanol, hydrocarbons, oxalic acid, and other valuable products. 

Et4N]2[Fe2lr2(CO)i2] cluster precursor, which exhibit a high activity in the synthesis of methanol from CO and H2, were studied by Ir and Fe Mossbauer spectroscopy. The study extends from the precursors via the fresh to the aged catalysts. The presence of iridium in the metallic state as well as the presence of trivalent, divalent and alloyed iron is detected. Representative Ir and Fe Mossbauer spectra are shown in Fig. 7.69. Information about the adsorption on the surface of MgO... 

Zinc oxide has various uses but the most important is as co-catalyst with CuO supported on A1203 for low-pressure synthesis of methanol from methane.325... 

Methanol production, where CO is added as additive, is very a well-known reaction. The production is carried out in two steps. The first step is to convert the feedstock natural gas into a synthesis gas stream consisting of CO, CO2, H20 and hydrogen. This is usually accomplished by the catalytic reforming of feed gas and steam. The second step is the catalytic synthesis of methanol from the synthesis gas. If an external source of C02 is available, the excess hydrogen can be consumed and converted to additional methanol. 

The gas-phase synthesis of methanol (M) from CO and H2 is a reversible reaction ... 

The synthesis of methanol, CO + 2H2 = CH3OH, like ammonia synthesis, is an exothermic, reversible, catalytic reaction. Unlike a catalyst for ammonia synthesis, a catalyst for... 

More recently, the direct synthesis of methanol from methane, using metallic gold as catalyst, was reported, involving a purported CH3-Au intermediate. Selenic acid was used as a stoichiometric oxidant as it is known to oxidize gold metal. Moderate turnovers (30) were achieved (Equation (6)).14... 

A paper by Szanyi and Goodman [56] on the synthesis of methanol over a copper single crystal provides a good example of how AES is often used in surface science studies of catalytic reactions. These authors investigated the formation of methanol from a mixture of CO2, CO and H2 on Cu(100) at tempera-... 

Figure 6.20 shows an example in which QEXAFS has been used in combination with XRD to study the temperature programmed reduction of copper oxide in a Cu/ZnO/Al203 catalyst for the synthesis of methanol [43,44]. Reduction to copper metal takes place in a narrow temperature window of 430-440 K, and is clearly revealed by both the EXAFS pattern and the appearance of the (111) reflection of metallic copper in the XRD spectra. Note that the QEXAFS detects the metallic copper at a slightly lower temperature than the XRD does, indicating that the first copper metal particles that form are too small to be detected by XRD, which requires a certain extent of long range order [43,44],... 

The activity and stability of skeletal catalysts can be improved with the use of additives, often referred to as promoters. These can be added to the alloy before leaching, or alternatively can be added to the leaching solution [16-19], An example is the use of zinc to promote skeletal copper for the catalytic synthesis of methanol from synthesis gas [20-22], Mary other promoters have been considered, both inorganic and organic in nature. 

A typical example for a reaction with substantial contraction of volume is the synthesis of methanol from syngas. Formally, 1 mol CO and 2 mol of H2 react to form 1 mol of methanol. This means that at high degrees of conversion, the contraction in volume can be a factor of three. This has dramatic implications for the pressure as the gas volume drops, the total pressure also drops. As a surplus, the analytical evaluation of the reaction is also complicated owing to the change in volume as a function of the degree of conversion. 

In the 1920s the catalytic synthesis of methanol was commercialized in Germany. Even before that, methane was distilled from wood, but this pyrolysis of wood was relatively inefficient. 

The process for synthesis of methanol involves these basic steps ... 

Water gas from which the CO has been removed is called synthesis gas because it can be used as a starting material for a variety of organic and inorganic compounds. For example, it can be used as the sotrrce of for the synthesis of methanol ... 

Syngas (typically a mixture of CO, H, and CO ) reacts over the active catalyst (Cu/Zn/AljOj) dispersed in an inert oil medium. This process offers considerable advantages over the conventional vapor phase synthesis of methanol in the areas of heat transfer, exothermicity, and selectivity toward methanol. However, this process suffers from the drawback that the methanol synthesis reaction is a thermodynamically governed equilibrium reaction. 

Table I details most of the recent developments regarding direct synthesis of methanol-higher alcohol mixtures.

Methanol was first produced commercially in 1830 by the pyrolysis of wood to produce wood alcohol. Almost a century later, a process was developed in Germany by BASF to produce synthetic methanol from coal synthesis gas. The first synthetic methanol plant was introduced by BASF in 1923 and in the United States by DuPont in 1927. In the late 1940s, natural gas replaced coal synthesis gas as the primary feedstock for methanol production. In 1966, ICI announced the development of a copper-based catalyst for use in the low-pressure synthesis of methanol. 

Recently Gao and Au (2000) have reported the synthesis of methanol from the hydrogenation of CO2 over YBa2Cu30y. The reactions suggest H2 adsorption at Cu sites and the adsorption of CO2 at the anion vacancies of the tetragonal phase formed during the catalytic reaction. 

Coal liquefaction Fischer-Tropsch synthesis Synthesis of methanol Hydrogenation of oils Alkylation of methanol and benzene Polymerization of olefins Hydrogenation of coal oils, heavy oil fractions, and unsaturated fatty acids Adsorption of S02 in an aqueous slurry of magnesium oxide and calcium carbonate S02 or removal from tail gas Wet oxidation of waste sludge Catalytic desulfurization of petroleum fractions Wastewater treatment... 

According to Poels, the interfacial active sites between Cu and ZnO play the key role in the synthesis of methanol.29... 

Since other possible transformations, such as, formation of dimethyl ether, higher alcohols, and hydrocarbons, are accompanied with higher negative free-energy change, methanol is thermodynamically a less probable product. Therefore, solely on a thermodynamic basis, these compounds as well as methane should be formed in preference to methanol. To avoid the formation of the former compounds, the synthesis of methanol requires selective catalysts and suitable reaction conditions. Under such conditions, methanol is the predominant product. This indicates that the transformations leading to the formation of the other compounds are kinetically controlled. In the methanol-to-hydrocarbon conversion, dimethyl ether generally is converted similarly to methanol. 

The low-pressure copper catalysts are very selective for the synthesis of methanol. Under industrial conditions on the Cu-Zn0-Al203 catalyst, the selectivity is typically greater than 99%. The impurities formed include hydrocarbons, higher alcohols, ethers, ketones, and esters. These, as well as any water formed, can easily be removed by distillation to give very pure methanol. 

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