Chemistry based on synthesis gas

The major route for the industrial production of vinyl acetate, the monomer of polyvinyl acetate (emulsion paints, adhesives) and its hydrolysis product, polyvinyl alcohol (textiles, food packaging) is closely related to the Wacker acetaldehyde process, but the industrial catalysts are heterogeneous. A mixture of ethene, oxygen and acetic acid is passed over a palladium catalyst supported on alumina at 100-200°C. The overall reaction is H C=CH2-hCHjCO H-hyO - H2C=CHC02CH3 -hH O. Ethene is no longer cheap, so that work is being pursued to make vinyl acetate from synthesis gas (p. 384). 

There is not space to discuss the details of syn. gas production here. The first reaction (steam reforming) is highly endothermic and involves an increase in entropy. It is carried out at high temperatures and moderate pressures (700-830°C/l5-40 atm) over a nickel catalyst supported on a-alumina or calcium aluminate and promoted by alkali metal oxides, which help to prevent the deposition of carbon. 

It is important to be able to control the ratio of carbon monoxide to hydrogen. This may be done via the water gas shift equilibrium 

This moves to the right as the temperature is lowered. Catalysts based on iron and chromium oxides (Fe30 on Cr O ) require temperatures of 400-500°C, leaving 2-4% CO in the reactant gas. More active catalysts (copper and zinc oxides) can be operated at 190-260°C but are easily poisoned. 

A summary of some of the chemicals which can be manufactured from syn. gas is given in Fig. 12.14. 

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A chemistry based on the conversion of synthesis gas has been developed and appHed extensively in South Africa to the production of Hquid fuels and many other products. A small-scale production is used in the manufacture of photographic film materials from coal-derived synthesis gas in the Eastman Kodak plant in Kingsport, Tennessee. However, the principal production of chemicals from coal involves the by-products of coke manufacturing. 

Figures 2, 3 and 4 offer an illustration of typical petrochemical complexes associated with industrial units based in the first case on synthesis gas chemistry, intended in the second to manufacture chiefly olefins and diolefms, and in the third to produce aromatic hydrocarbons.

The shift from coal to oil, of course, had major consequences for the chemical industry. Alkenes, instead of synthesis gas and acetylene, became the basic building blocks. Homogeneous catalysis became increasingly important for the production of chemicals. We already mentioned the Reppe chemistry, based on acetylene as the main feedstock. In 1938, the same year that Reppe started his work, another German scientist, Otto Roelen, discovered the reaction of olefins with carbon monoxide and hydrogen over a cobalt carbonyl catalyst to form aldehydes, known... 

In considering the chemical reactions based on the light olefins it is obvious that natural gas liquids are at a disadvantage in comparison with the corresponding refinery cuts. These contain varying but substantial percentages of olefins as such—the results of thermal and catalytic decomposition of the heavier petroleum molecules. But refinery olefins are also in demand for synthesis to premium motor fuels. It is fortunate that there are abundant supplies of natural gas paraffins for conversion to provide adequate raw material for our olefin chemistry. 

Reasons for interest in the catalyzed reactions of NO, CO, and COz are many and varied. Nitric oxide, for example, is an odd electron, hetero-nuclear diatomic which is the parent member of the environmentally hazardous oxides of nitrogen. Its decomposition and reduction reactions, which occur only in the presence of catalysts, provide a stimulus to research in nitrosyl chemistry. From a different perspective, the catalyzed reactions of CO and COz have attracted attention because of the need to develop hydrocarbon sources that are alternatives to petroleum. Carbon dioxide is one of the most abundant sources of carbon available, but its utilization will require a cheap and plentiful source of hydrogen for reduction, and the development of catalysts that will permit reduction to take place under mild conditions. The use of carbon monoxide in the development of alternative hydrocarbon sources is better defined at this time, being directly linked to coal utilization. The conversion of coal to substitute natural gas (SNG), hydrocarbons, and organic chemicals is based on the hydrogen reduction of CO via methanation and the Fischer-Tropsch synthesis. Notable successes using heterogeneous catalysts have been achieved in this area, but most mechanistic proposals remain unproven, and overall efficiencies can still be improved. 

Coal was also the feedstock for synthesis gas vide infra). Many contributions to acetylene chemistry are due to Reppe. His work on new homogeneous metal (mainly nickel) catalysts for acetylene conversion, carried out in the period from 1928 to 1945, was not published until 1948. Under the influence of nickel iodide catalysts, acetylene, water and CO were found to give acrylic acid. A process based on this chemistry was commercialized in 1955. 

Chun, H., Dybstev, D.N., Kim, H., and Kim, K. 2005. Synthesis, x-ray crystal structures, and gas sorption properties of pillared square grid nets based on paddle-wheel motifs Implications for hydrogen storage in porous materials. Chemistry—A European Journal 11, 3521-3529. 

A few chemicals are based on the direct reaction of methane with other reagents, including carbon disulfide, hydrogen cyanide, chloromethanes, and synthesis gas mixture. A more detailed discussion for chemistry and synthesis can be found in Chapter 4. In this chapter, emphasis will be placed on the environmental aspects of the chemicals and their manufacturing technologies. 

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