Uses of Synthesis Gas

Synthesis gas is an important intermediate. The mixture of carbon monoxide and hydrogen is used for producing methanol. It is also used to synthesize a wide variety of hydrocarbons ranging from gases to naphtha to gas oil using Fischer Tropsch technology. This process may offer an alternative future route for obtaining olefins and chemicals. The hydroformylation reaction (Oxo synthesis) is based on the reaction of synthesis gas with olefins for the production of Oxo aldehydes and alcohols (Chapters 5, 7, and 8). 

Synthesis gas is a major source of hydrogen, which is used for producing ammonia. Ammonia is the host of many chemicals such as urea, ammonium nitrate, and hydrazine. Carbon dioxide, a by-product from synthesis gas, reacts with ammonia to produce urea. 

The production of synthesis gas from methane and the major chemicals based on it are noted in Chapter 5. 

Hydrocarbons from Synthesis Gas (Fischer Tropsch Synthesis, FTS) 

Most of the production of hydrocarbons by Fischer Tropsch method uses synthesis gas produced from sources that yield a relatively low 

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Occurrence. Carbon monoxide is a product of incomplete combustion and is not likely to result where a flame bums in an abundant air supply, yet may result when a flame touches a cooler surface than the ignition temperature of the gas. Gas or coal heaters in the home and gas space heaters in industry have been frequent sources of carbon monoxide poisoning when not provided with effective vents. Gas heaters, though properly adjusted when installed, may become hazardous sources of carbon monoxide if maintained improperly. Automobile exhaust gas is perhaps the most familiar source of carbon monoxide exposure. The manufacture and use of synthesis gas, calcium carbide manufacture, distillation of coal or wood, combustion operations, heat treatment of metals, fire fighting, mining, and cigarette smoking represent additional sources of carbon monoxide exposure (105—107). 

Other Methods of Preparation. In addition to the direct hydration process, the sulfuric acid process, and fermentation routes to manufacture ethanol, several other processes have been suggested. These include the hydration of ethylene by dilute acids, the hydrolysis of ethyl esters other than sulfates, the hydrogenation of acetaldehyde, and the use of synthesis gas. None of these methods has been successfilUy implemented on a commercial scale, but the route from synthesis gas has received a great deal of attention since the 1974 oil embargo. 

Synthesis Ga.s, Since petroleum prices rose abmpdy in 1974, the production of ethanol from synthesis gas, a mixture of carbon monoxide and hydrogen, has received considerable attention. The use of synthesis gas as a base raw material has the same drawback as fermentation technology low yields limited by stoichiometry. 

Synthesis gas consists of a nonhydrocarhon mixture (H2,CO) ohtain-ahle from more than one source. It is included in this chapter and is further noted in Chapter 5 in relation to methane as a major feedstock for this mixture. This chapter discusses the use of synthesis gas obtained from coal gasification and from different petroleum sources for producing gaseous as well as liquid hydrocarbons (Fischer Tropsch synthesis). 

The system is not limited to the use of synthesis gas as feed. Mixtures of carbon dioxide and hydrogen also give rise to the formation of polyhydric alcohols, and it is also claimed that the reaction mixture can consist of steam and carbon monoxide (62). This latter claim is consistent with the presence of C02 in the reaction mixture when CO/H2 is used as feed [infrared data (62)], and suggests that these ionic rhodium systems are also active catalysts for the water gas-shift reaction (vide infra). 

The most important uses of synthesis gas are the manufacture of ammonia (NH3) via the Haber process. A mixture of nitrogen and hydrogen are passed over an iron catalyst (with aluminum oxide present as a "promoter"). The operating conditions are extreme—800°F and 4000 psi,... 

The rapidly growing world concern over future oil supplies has led to considerable research activity into the use of synthesis gas or synthesis gas-derived molecules, such as methanol, as future feedstock materials for... 

A critical prerequisite for the use of synthesis gas or CO in most reactions catalyzed by transition metals is that sulfur compounds, such as H2S, thiols, or COS, derived from the sulfur content of crude oil or coal must first be removed (hydrodesulfurization, see Section 21-4). 

Carbonylation of methyl acetate, developed in particular by Hakoru This method is based on the use of synthesis gas to produce successively methanol, methyl acetate, and acetic anhydride jointly with ethyiidene diacetate, which then decomposes to vinyl acetate and acetic add, which is recycled to methyl acetate synthesis. The overall reaction is the following ... 

Much exploratory research is being conducted involving concepts for the direct conversion of methane to a liquid hydrocarbon fuel without the use of synthesis gas. The following concepts have reached the stage where realistic engineering and economic evaluations are possible ... 

An extension of the technology associated with carbonylation of methyl acetate, namely the use of synthesis gas rather than CO alone, enables the production of other members of the acetyl chemicals family, in particular ethyl acetate, and the important monomer, vinyl acetate, via a pivotal intermediate ethylidene diacetate (1,1-diacetoxyethane). 

In the following sections, the applications for synthesis gas will be summarized, the chemistry and thermodynamics related to the production of synthesis gas will be described and after which the various industrial processes for the manufacture of synthesis gas will be highlighted. The emphasis will be on catalytic routes, but thermal (partial oxidation) routes will be briefly described as well. Carbon capture and sequestration (CCS) is added, as this is an increasingly important issue for the use of synthesis gas as a source for hydrogen as an energy vector. 

One particular emerging trend in applications is related to the use of synthesis gas in the context of a possible hydrogen economy. This will be the topic of the next paragraph in this article. 

Recently, substantial research activity has been conducted in the area of CH4 conversion without the use of synthesis gas. We classify such processes as "Direct Methane Conversion." They have the potential of being more energy-efficient since they bypass the energy-intensive step of synthesis gas formation. 

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