Alternative Feedstocks for Synthesis

Behr A, Johnen L (eds) (2012) Alternative feedstocks for synthesis, vol 7. Handbook of green chemistry. Wiley, Weinheim (in print)... 

In the 1970s, the oil crisis generated a need for alternative raw materials. Coal and especially natural gas were reconsidered as carbon sources. Synthesis gas, now produced from natural gas, became an alternative feedstock for the production of oxygenated hydrocarbons. For instance, a new process employing organorhodium compounds was developed to produce acetic anhydride from synthesis gas via carbonylation of methyl acetate. 

This excess hydrogen is normally carried forward to be compressed into the synthesis loop, from which it is ultimately purged as fuel. Addition of by-product CO2 where available may be advantageous in that it serves to adjust the reformed gas to a more stoichiometric composition gas for methanol production, which results in a decrease in natural gas consumption (8). Carbon-rich off-gases from other sources, such as acetylene units, can also be used to provide supplemental synthesis gas. Alternatively, the hydrogen-rich purge gas can be an attractive feedstock for ammonia production (9). 

Feedstock for Chemical Synthesis. It is estimated that <0.5% of the sucrose produced each year is used for nonfood purposes (41). An alternative appHcation, namely the production of chemicals, is an attractive option as the feedstock is plentiful, renewable, and of consistently high purity. Moreover, the biodegradabiUty of many sucrochemicals makes them environmentally friendly. 

The catalytic activation of carbon monoxide is a research area currently receiving major attention from academic, industrial, and government laboratories. There has been a long standing interest in this area however, the new attention obviously is stimulated by concerns with the present and future costs and availability of petroleum as a feedstock for the production of hydrocarbon fuels and of organic chemicals. One logical alternative source to be considered is synthesis gas, mixtures of carbon monoxide and hydrogen that can be produced from coal and other carbonaceous materials. 

Electrochemical reduction and oxidation processes offer several advantages over conventional methods in their application to organic synthesis. For example, selective transformations can be carried out on specific groups in a multifunctional, valuable compound under the usually mild reaction conditions. Independence of a reagent will result in drastically diminished environmental problems by spent reagents. Electrochemistry also allows the application of alternative feedstocks and better use of raw materials. Product isolation and continuous processing are simplified. 

Thus, as technologies develop in all these areas of ammonia synthesis gas generation, there will be a new set of guidelines for analyzing the relative economics of alternate feedstocks. 

Presuming market prices are competitive, one route to development of larger markets for biomass in polymeric products is to convert biomass feedstocks to the same monomers that are used for synthesis of the large-volume polymers and copolymers from fossil-derived monomers. An alternative is to discover and develop natural and synthetic biopolymers that have superior or unique properties. Each of these approaches is discussed in the next section. 

From a commercial point of view, organic halides are in principle a less attractive feedstock for the synthesis of alkanoic or benzoic acid derivatives compared with alkenes or toluenes, which can lead to the corresponding acids via hydroformyla-tion and oxidation, hydrocarboxylation, or direct air oxidation, respectively. Thus, apart from methanol, an economically viable carbonylation of C-X compounds is restricted to the synthesis of higher-value fine chemicals in cases where alternative starting materials are not easily accessible, e. g., phenylacetic acid derivatives (cf. Section 2.1.2.1). 

The U.S. currently imports about sixty (60) percent of its oil requirements (7), which is expected to increase to about 70 percent by the year 2025 (7). This reliance on foreign sources of oil has created both national and economic security issues for the U.S. It is desirable to produce liquid transportation fuels from alternative sources. The Fischer-Tropsch (F-T) process can be used to produce liquid fuels from synthesis gas (syngas), a mixture of hydrogen and carbon monoxide. Liquid fuels produced from die F-T process have very low levels of sulfur compared to petroleum products these ultra-clean fuels are environmentally friendly. However, syngas is commonly produced from natural gas, which has become significantly more expensive in recent years (2). Alternative, less expensive feedstocks for syngas production can reduce the costs of liquid fuels produced through the F-T process. 

TTistorically, the sources of petrochemical feedstocks have been related directly to the supply of petroleum. Initially, liquified petroleum gases (LPG) supplied this need. Later, as the supply of LPG diminished, naphthas became the primary source (I). The 1973 Arab oil embargo dramatically demonstrated the critical need for alternative sources of fossil carbon. Thus, any development to reduce our dependence on foreign suppliers of petroleum, e.g., an economic coal-based process, should have high priority (2). Hence, there has been a renewal of interest in Fischer-Tropsch processes (3-i4), the catalytic synthesis of primarily C5-C11 hydrocarbons from CO-H2 mixtures. Unfortunately, economic considerations indicate that a synthetic naphtha as cracker feedstock for... 

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