Synthesis gas to methanol

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. 

A steam reformer is a large process furnace possessing a series of externally heated, catalyst-filled reaction tubes. The principal reaction taking place in the steam reformer produces a synthesis gas represented by the following equation  

Special high-strength metallurgy is used in the construction of reformer tubes to help ensure longer life and better efficiency. 

Process gases leaving the steam reformer are at temperatures of about 1580°F to 1,620°F (860°C to 880°C). This heat is recovered in heat exchange systems for use in boilers and overall process applications. 

Synthesis gas is compressed to pressures of about 250 psig before entering the methanol synthesis reactor and conversion to methanol. Also, after methanol synthesis, any unreacted synthesis gas is again compressed and recycled back through the reactor. 

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Eastman Chemical Company has operated a coal-to-methanol plant in Kingsport, Tennessee, since 1983. Two Texaco gasifiers (one is a backup) process 34 Mg/h (37 US ton/h) of coal to synthesis gas. The synthesis gas is converted to methanol by use of ICl methanol technology. Methanol is an intermediate for producing methyl acetate and acetic acid. The plant produces about 225 Gg/a (250,000 US ton/a) of acetic anhydride. As part of the DOE Clean Coal Technology Program, Air Products and Cnemicals, Inc., and Eastman Chemic Company are constructing a 9.8-Mg/h (260-US ton/d) slurry-phase reactor for the conversion of synthesis gas to methanol and dimethyl... 

Shortly after World War I, Badische Amlin patented the catalytic conversion of synthesis gas to methanol, and Fischer and Tropsch (F-T) announced a rival process in which an iron catalyst converted synthesis gas into a mixture of oxygenated hydrocarbons. Later,... 

The double arrows in the methanol reaction indicate that the reaction can go in either direction. There is a principle here that is taught in the sophomore P-chem class (Physical chemistry) of every chemical engineer. Methanol, in the vapor state, takes up only one-third the volume as the equivalent amounts of CO and H2. So in order to "push the reaction to the right," the process is run under pressure. That causes the compound that takes up less volume to be favored—synthesis gas to methanol rather than methanol to synthesis. 

The first commercial plant that converted synthesis gas to methanol was built in 1924 in Germany by BASF. It ran at very high pressures (3500—5000 psi) and used a zinc-copper catalyst. In the years since then, further development of catalysts has brought the pressures down, eliminating much of... 

Methanol Synthesis. The transformation of synthesis gas to methanol [Eq. (3.3)] is a process of major industrial importance. From the point of view of hydrocarbon chemistry, the significance of the process is the subsequent conversion of methanol to hydrocarbons (thus allowing Fischer-Tropsch chemistry to become more selective). 

The current two-step industrial route for the synthesis of methanol, from coal or methane to synthesis gas and then from synthesis gas to methanol, has certain drawbacks. The economic viability of the whole process depends on the first step, which is highly endothermic. Thus a substantial amount of the carbon source is burned to provide the heat for the reaction. It would be highly desirable, therefore, to replace this technology with a technically simpler, single-step process. This could be the direct partial oxidation of methane to methanol, allowing an excellent way to utilize the vast natural-gas resources. Although various catalysts, some with reasonable selectivity, have been found to catalyze this reaction (see Sections 9.1.1 and 9.6.1), the very low methane conversion does not make this process economically feasible at present. 

The conventional methanol synthesis is a three-stage process that involves the following steps (1) Catalytic reforming of CH4 by steam—a very endothermic process leading to a synthesis gas consisting of CO, C02 and H2 (2) shift reaction (CO + H20 C02 + H2) to obtain the desired molar ratios H2/CO and H2/C02 and (3) catalytic conversion of synthesis gas to methanol. 

A possible solution is to gasify the more dilute vacuum tower bottoms product in an oxygen blown gasifier and to convert the excess synthesis gas to methanol. In those cases where a Flexicoker is used the heavy scrubber liquids could be recycled to extinction. Therefore, the plant products are SNG, naphtha, 300-800°F distillate and methanol. All of these products are of high quality or can be hydrotreated to achieve high quality. As a result, they could be easily integrated into the utility fuel mix with a minimum amount of disruption or special product handling facilities. 

The conversion efficiency of the synthesis gas-to-methanol step is about 85%, and it is usually assumed that improved catalytic gasification techniques are required to raise the overall conversion efficiency above the 51% mentioned above (Faaij and Hamelinck, 2002). The total efficiency will become lower if all life-cycle contributions involving energy inputs, e.g. for collecting and transporting biomass, are included (EC, 1994). 

The overall results are very encouraging and the production of a synthesis gas may be cautiously projected from the experimental work. The processing steps from the synthesis gas to methanol, ammonia or hydrocarbons are relatively straightforward. 

Several processing alternatives have been proposed for converting synthesis gas to methanol. The main incentives are reduced energy costs due to the ability to operate at lower temperatures, lower pressures or both. The most notable of these alternatives (in terms of recent interest) have been the alkyl formate process (ref. 27) and the Chem Systems three-phase reactor approach (ref. 28). A very recent development is the use of a gas-solid-solid trickle flow reactor.which it is proposed can be retrofitted in conventional low pressure methanol synthesis plants (ref. 29). These three alternatives will be reviewed in turn. 

Mention should be made of our concern about distribution costs. The DOE position papers gloss over distribution costs of alcohol/gasoline fuels. Also overlooked is the possible economic gain by going from coal to synthesis gas to methanol to gasoline using the Mobil process for the latter route (8). This couid avoid the probiem of new storage faciiities and get around the need for another fuei distribution system. 

Most organic chemicals are currently made commercially iixim ethylene, a product of oil lehning. It is possible that in the next several decades we may have to shift toward other carbon sources for these chemicals as depletion of our oil reserves continues. Either coal or natural gas (methane) can be converted into CO/Hz mixtures with mr and steam (Eq. 12.18), and it is possible to convert such mixtures, variously called water-gas or synthesis gas to methanol (Eq. 12.18) and to allume fuels with various heterogeneous catadysts. In particular, the Fischer-Tropsch reaction (Eq. 12.19) converts synthesis gas to a mixture of long-chain alkanes and alcohols using heterogeneous catalysts. 

Gotti, A. and Prins, R. Basic metal oxides as co-catalysts in the conversion of synthesis gas to methanol on supported palladium catalysts. J. Catal. 1998,175, 302-311. 

Gotti, A. Prins, R. Basic Metal Oxides as Cocatalysts for Cu/SiO Catalysts in the Conversion of Synthesis Gas to Methanol. J. Catal. 1998, 178,511-519. 

This chapter shows that alcohol production via synthesis gas is common practice for methanol, but not for higher alcohols. However, the synthesis gas comes from fossil sources (mainly namral gas), making the use of methanol for fuel purposes not very attractive compared to existing fossil-fuel-based options. A bio-based synthesis gas to methanol process is being developed in which biomass waste streams are being used as a source of synthesis gas. Alternatively, biomethane (biogas) could be used as a bio-based resource for methanol. The latter can also be used as a resource for the production of ethanol via the OCM process to ethane/ethylene mixtures. The ethylene can be converted chemically into ethanol via the existing catalytic hydration process or, if further developed, the ethane formed can be catalytically converted into ethanol with the aid of N2O. 

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